New auto-open feature from Bo Peng (with help from Jean-Marc and Enrico)

New auto-open feature from Bo Peng (with help from Jean-Marc and Enrico)

	* src/lyx_main.C (init): call Formats::setAutoOpen.

	* src/lyxrc.C (read): do not reset editor/viewer values of "none".

	* src/format.C (fixCommand): helper function: tweak command depending
	of the availability of OS viewer/editor.
	(setAutoOpen): run fixCommand over all the formats.

	* src/support/Makefile.am: under win32, link against shlwapi.dll.

	* src/support/os_*.C (canAutoOpenFile, autoOpenFile): new
	functions, used	to let the OS handle viewers and editors it knows about.

	* configure.ac: improve check for shlwapi.

	* lib/configure.py: remove check for native windows viewers.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@13855 a592a061-630c-0410-9148-cb99ea01b6c8