Work around the broken formatting of sys.ps1 prompts in running text.

Move sample sessions to the left margin of the file for consistency;
formatting can adjust the margin if needed.

This closes SF bug #133213.

Doc/lib/libdoctest.tex

@@ -226,11 +226,11 @@ No problem, as long as the only output generated by the example is the
 traceback itself.  For example:
 
 \begin{verbatim}
-    >>> [1, 2, 3].remove(42)
-    Traceback (most recent call last):
-      File "<stdin>", line 1, in ?
-    ValueError: list.remove(x): x not in list
-    >>>
+>>> [1, 2, 3].remove(42)
+Traceback (most recent call last):
+  File "<stdin>", line 1, in ?
+ValueError: list.remove(x): x not in list
+>>>
 \end{verbatim}
 
 Note that only the exception type and value are compared (specifically,
@@ -257,26 +257,27 @@ tabs and spaces if you're too lazy to do it right, but doctest is not in
 the business of guessing what you think a tab means).
 
 \begin{verbatim}
-    >>> # comments are ignored
-    >>> x = 12
-    >>> x
-    12
-    >>> if x == 13:
-    ...     print "yes"
-    ... else:
-    ...     print "no"
-    ...     print "NO"
-    ...     print "NO!!!"
-    ...
-    no
-    NO
-    NO!!!
-    >>>
+>>> # comments are ignored
+>>> x = 12
+>>> x
+12
+>>> if x == 13:
+...     print "yes"
+... else:
+...     print "no"
+...     print "NO"
+...     print "NO!!!"
+...
+no
+NO
+NO!!!
+>>>
 \end{verbatim}
 
-Any expected output must immediately follow the final \code{">>>"} or
-\code{"..."} line containing the code, and the expected output (if any)
-extends to the next \code{">>>"} or all-whitespace line.
+Any expected output must immediately follow the final
+\code{'>\code{>}>~'} or \code{'...~'} line containing the code, and
+the expected output (if any) extends to the next \code{'>\code{>}>~'}
+or all-whitespace line.
 
 The fine print:
 
@@ -310,8 +311,9 @@ yes
             1.0
 \end{verbatim}
 
-and as many leading whitespace characters are stripped from the expected
-output as appeared in the initial ">>>" line that triggered it.
+and as many leading whitespace characters are stripped from the
+expected output as appeared in the initial \code{'>\code{>}>~'} line
+that triggered it.
 \end{itemize}
 
 \subsection{Warnings}
@@ -349,26 +351,26 @@ testmod skips it by default.  Other approaches are described in
 % Hey! What happened to Monty Python examples?
 % Tim: ask Guido -- it's his example!
 \begin{verbatim}
-    >>> foo()
-    {"Hermione": "hippogryph", "Harry": "broomstick"}
-    >>>
+>>> foo()
+{"Hermione": "hippogryph", "Harry": "broomstick"}
+>>>
 \end{verbatim}
 
 is vulnerable!  One workaround is to do
 
 \begin{verbatim}
-    >>> foo() == {"Hermione": "hippogryph", "Harry": "broomstick"}
-    1
-    >>>
+>>> foo() == {"Hermione": "hippogryph", "Harry": "broomstick"}
+1
+>>>
 \end{verbatim}
 
 instead.  Another is to do
 
 \begin{verbatim}
-    >>> d = foo().items()
-    >>> d.sort()
-    >>> d
-    [('Harry', 'broomstick'), ('Hermione', 'hippogryph')]
+>>> d = foo().items()
+>>> d.sort()
+>>> d
+[('Harry', 'broomstick'), ('Hermione', 'hippogryph')]
 \end{verbatim}
 
 There are others, but you get the idea.
@@ -376,9 +378,9 @@ There are others, but you get the idea.
 Another bad idea is to print things that embed an object address, like
 
 \begin{verbatim}
-    >>> id(1.0) # certain to fail some of the time
-    7948648
-    >>>
+>>> id(1.0) # certain to fail some of the time
+7948648
+>>>
 \end{verbatim}
 
 Floating-point numbers are also subject to small output variations across
@@ -386,20 +388,20 @@ platforms, because Python defers to the platform C library for float
 formatting, and C libraries vary widely in quality here.
 
 \begin{verbatim}
-    >>> 1./7  # risky
-    0.14285714285714285
-    >>> print 1./7 # safer
-    0.142857142857
-    >>> print round(1./7, 6) # much safer
-    0.142857
+>>> 1./7  # risky
+0.14285714285714285
+>>> print 1./7 # safer
+0.142857142857
+>>> print round(1./7, 6) # much safer
+0.142857
 \end{verbatim}
 
 Numbers of the form \code{I/2.**J} are safe across all platforms, and I
 often contrive doctest examples to produce numbers of that form:
 
 \begin{verbatim}
-    >>> 3./4  # utterly safe
-    0.75
+>>> 3./4  # utterly safe
+0.75
 \end{verbatim}
 
 Simple fractions are also easier for people to understand, and that makes