Add MCNAME: an equivalent of MCSTR for NameRefs

Does exactly what it says on the tin.
Stack loading code now uses StringRefs/NameRefs
Replaced MCmessagenamestring with MCN_messagename
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_findstack

Conflicts:
	engine/src/dispatch.cpp
Fix errors and oversights
Yet more (attempted) fixes
More corrections
Fix a potential assertion failure
Replace an incorrect check for an empty string
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_findstack

Conflicts:
	engine/src/stack.h
Fix an excess MCValueRetain() call
Merge branch 'refactor-syntax_unicode_findstack' into refactor-syntax_unicode
Merge branch 'refactor-syntax_unicode' of https://github.com/runrev/livecode into refactor-syntax_unicode