[configure] Add check for Mono 2.10.9 at config time

As it is said in BXC#11134, MonoDevelop depends on Mono 2.10.9 or newer
so then the configure phase should fail with a friendly error rather than
having a cryptic compiler error.
Fixed 'Bug 11110 - SQL syntax highlighting broken'.
Fixed 'Bug 11108 - Find in files dialog requires use wildcard'.
Fixed 'Bug 11085 - Rename incorrectly renames shadowed parent member '
Fixed 'Bug 11116 - Click rapidly on scrollbar in source navigation
dropdowns causes window to close'.
Fixed 'Bug 10966 - New line break injects into collapsed code'.
[CSharpBinding] Created properties are now public.
Fixed 'Bug 11149 - Code generation window only shows Property
Generation options for variables that start with lowercase letters'.
Merge pull request #255 from knocte/config_fixes

[configure] Add check for Mono 2.10.9 at config time
Revert "Upgrade sln to VS 2012"

This reverts commit 0c4cf6beca91d3b9a9f5ca2d91019fef05d9c351.
I need to be able to compile in VS2010.

Conflicts:
	main/external/cecil