Update to work with Xtext 2.3.1 / Eclipse 4.2 Juno
Change execution environment from J2SE-1.5 to JavaSE-1.6
Refactor code using catches for control flow

Especially in the building & scoping sections
Fix exception issue with dummy resource for projections
Update version to 1.5.3
Merge branch 'master' of github.com:GrammaticalFramework/gf-eclipse-plugin

Conflicts:
	workspace/org.grammaticalframework.eclipse.tests/META-INF/MANIFEST.MF
	workspace/org.grammaticalframework.eclipse/META-INF/MANIFEST.MF
	workspace/org.grammaticalframework.eclipse/src-gen/org/grammaticalframework/eclipse/services/GFGrammarAccess.java
Fix buttons and use of deprecated method in Project prefs.

Other small tinkering.
Some better catching of exceptions.