Closes #1215: document better why it is not a good idea to catch e.g. SIGSEGV…

Closes #1215: document better why it is not a good idea to catch e.g. SIGSEGV and refer to faulthandler.

Patch by Martin Pool.

Doc/library/signal.rst

@@ -36,7 +36,11 @@ at a later point(for example at the next :term:`bytecode` instruction).
 This has consequences:
 
 * It makes little sense to catch synchronous errors like :const:`SIGFPE` or
-  :const:`SIGSEGV`.
+  :const:`SIGSEGV` that are caused by an invalid operation in C code.  Python
+  will return from the signal handler to the C code, which is likely to raise
+  the same signal again, causing Python to apparently hang.  From Python 3.3
+  onwards, you can use the :mod:`faulthandler` module to report on synchronous
+  errors.
 
 * A long-running calculation implemented purely in C (such as regular
   expression matching on a large body of text) may run uninterrupted for an

Misc/ACKS

@@ -974,6 +974,7 @@ Oleg Plakhotnyuk
 Remi Pointel
 Guilherme Polo
 Michael Pomraning
+Martin Pool
 Iustin Pop
 Claudiu Popa
 John Popplewell