Patch by Berker Peksag

#17572: Avoid chained exceptions while passing bad directives to time.strptime().  Initial patch by Claudiu Popa.

Patch by Thomas Heller.

Patch by Thomas Heller.

when possible

Write a function to enable more optimizations:

 * If the substring is the whole string and overallocation is disabled, just
   keep a reference to the string, don't copy characters
 * Avoid a call to the expensive _PyUnicode_FindMaxChar() function when
   possible

Add an unit test to ensure that text files are rejectect (with TypeError)

Add an unit test to ensure that text files are rejectect (with TypeError)

We don't put coverage directives in the stdlib, but anyone looking at a
coverage report for Random should see the comment and understand why the lines
aren't covered.

Patch by Victor Terrón.

This was already done in Python3, but having it wrong leads to
incorrect debug output, so it seems worth fixing in 2.7 as well.

Patch by Victor Terrón.