All the new information in 3.4's readme.txt was already here, but the
wrong name was used to refer to the script.  Also reworded the sentence.

It now recommends PCbuild/get_externals.bat instead of the scripts in
Tools/buildbot.

I would just outright delete them, but the readme in PCbuild recommended
their use, so I figure it would be nice to leave them there for a while.

Back porting changeset db302b88fdb6 to 3.4 branch, which fixed multiple documentation typos.

Related Issues:
#issue21528
#issue24453

Related Issues:

#issue21528
#issue24453

and set comparisions.  Patch by Gareth Rees.

* Don't use the timestamp of an existing file anymore, only use fixed
  timestamp
* Enhance the code checking the resolution of the filesystem timestamps.
* Check timestamps with a resolution of 1 microsecond instead of 1 millisecond
* When os.utime() uses the current system clock, tolerate a delta of 20 ms.
  Before some os.utime() tolerated a different of 10 seconds.
* Merge duplicated tests and simplify the code

* Don't use the timestamp of an existing file anymore, only use fixed
  timestamp
* Enhance the code checking the resolution of the filesystem timestamps.
* Check timestamps with a resolution of 1 microsecond instead of 1 millisecond
* When os.utime() uses the current system clock, tolerate a delta of 20 ms.
  Before some os.utime() tolerated a different of 10 seconds.
* Merge duplicated tests and simplify the code

* Don't use the timestamp of an existing file anymore, only use fixed
  timestamp
* Enhance the code checking the resolution of the filesystem timestamps.
* Check timestamps with a resolution of 1 microsecond instead of 1 millisecond
* When os.utime() uses the current system clock, tolerate a delta of 20 ms.
  Before some os.utime() tolerated a different of 10 seconds.
* Merge duplicated tests and simplify the code