Fix two filename bugs (from Enrico and me)

Fix two filename bugs (from Enrico and me)

	* src/support/filetools.[Ch]
	(fileOpenSearch): comment out since it is unused
	(fileSearch): Use addExtension instead of changeExtension, since we
	are always called without extesnion, or with the correct one.
	(addExtension): new function

	* src/lyx_main.C
	(LyX::init): tell fileSearch that we are also interested in the name
	if the file does not exist

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16361 a592a061-630c-0410-9148-cb99ea01b6c8