Refine the documentation of Flymake

Refine the documentation of Flymake

* progmodes/flymake.el (flymake-save-buffer-in-file)
(flymake-makehash, flymake-posn-at-point-as-event, flymake-nop)
(flymake-selected-frame, flymake-log, flymake-ins-after)
(flymake-set-at, flymake-get-buildfile-from-cache)
(flymake-add-buildfile-to-cache, flymake-clear-buildfile-cache)
(flymake-find-possible-master-files, flymake-save-buffer-in-file):
Refine the doc string.
(flymake-get-file-name-mode-and-masks): Reformat.
(flymake-get-real-file-name-function): Fix a minor bug.

* flymake.texi: Changing from one space between sentences to two.