[msbuild] Improved the way it looks for the compiler (BooToolPath,
BooBinPath)

[msbuild] Make the Nant build fail if Boo MSBuild can't be compiled
No need to target net-2.0 for msbuild task anymore
Some error messages are reported as importange High instead of Normal
Merge pull request #72 from drslump/xbuild-mono-3-fix

[msbuild] improvements
update binaries
Merge master