Rename python function thread_from_thread_handle to thread_from_handle

Rename python function thread_from_thread_handle to thread_from_handle

This renaming was done to stay consistent with the naming of the new
gdb.InferiorThread.handle method.  I had initially named it "thread_handle"
but Tom Tromey suggested just "handle".

The old name (thread_from_thread_handle) still works, but is marked as
deprecated in comments in the code as well as in the documentation.

I have some code which uses these functions.  I very much like the
brevity of the new names.

gdb/doc/ChangeLog:

	* python.texi (Inferiors In Python): Rename
	Inferior.thread_from_thread_handle to Inferior.thread_from_handle.
	Add note about the former being deprecated.

gdb/ChangeLog:

	* python/py-inferior.c (infpy_thread_from_thread_handle):
	Adjust comments to reflect renaming of thread_from_thread_handle
	to thread_from_handle.  Adjust keywords.  Fix type error message.
	(inferior_object_methods): Add thread_from_handle.  Retain
	thread_from_thread_handle, but mark it as deprecated.

testsuite/ChangeLog:

	* gdb.python/py-thrhandle.exp: Adjust tests to call
	thread_from_handle instead of thread_from_thread_handle.