The "single instance" patch.

The "single instance" patch.

By default, if the lyxpipe is set up and working, loading of documents
is deferred to an already running instance. Note that an already running
instance is only used for loading, such that export from command line
still works as usual.

The default behavior can be changed through a preference setting, and,
whatever the default is, it can be overridden by command line options.
Unticking the "Single instance" check box in the preferences, LyX behaves
exactly as before the introduction of this feature.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@36278 a592a061-630c-0410-9148-cb99ea01b6c8