Improve the implementation unit System.Unwind.Raising
Merge branch 'master' (gcc-4.7, commit 'e039af4') into gcc-4.6

Conflicts:
	source/s-unwrai.adb

Modifications:
	source/s-unwrai.adb
	source/s-finimp.adb
Add Raise_Exception_From_Here to optimize raising an exception with a source location
Merge branch 'master' (gcc-4.7, commit 'd072af1') into gcc-4.6

Conflicts:
	source/s-unwrai.adb

Modifications:
	source/s-unwrai.adb