Update upgradingFromPreviousVersionsOfGrails.gdoc
GRAILS-10432: RESTful url mappings documentation should use includes/excludes
fix unintended strikethrough in commandLine forkedMode documentation

In the section heading for "Debugging and Forked Execution (--debug vs --debug-fork)",
the double-hyphens before the --debug and --debug-fork were not being rendered correctly,
and debug was being rendered as a strikethrough.  This change appears to result in the
intended rendering.
GRAILS-9927: uri attribute in createLink
GRAILS-10551: Document breaking change for integration tests
Fix escaping issue in GRAILS-10551 commit
Upgrade build to Gradle 1.8.
Fix exceptions during HTML generation.
Fix exception in PDF creation.
Fix PDF overflow so its readable.
Update sample BuildConfig.groovy to correct version.
Explain Spock changes for Grails 2.3.

This helps with issue GRAILS-10581. The upgrade notes now explain that Grails
comes with Spock support built in, so users should no longer use the Spock
plugin.

I have also added a summary list of the changes, making it easier to see all
of them in one go.
Merge branch '2.3.x'