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)