Reenable pkgconfig check for mono, but reducing bloat

In case you need a clarification wrt bloat:
http://tirania.org/blog/archive/2012/Oct-20.html
configure.ac: Mono 2.11.5 == 3.0

Mono version 2.11.5 was never released and was actually renamed to 3.0
protect against a null condition if no DefineConstants is present
merge update to F# power pack original sources
reduce noise during build
fix build break
copy and install xml files

This gives documentation for FSharp.Core.dll in MonoDevelop
Fixed a typo
Merge pull request #58 from vishnumenon/master

Fixed a typo in the README
Install docs for FSharp.Core 2.0
Build and install FSharp.Core 2.1 profile by default

This includes adding dependencies for the Mono profile 2.1 binaries we
need to reference
Merge branch 'master' of https://github.com/fsharp/fsharp
Add notes to README.md about what's produced by build
Merge https://github.com/fsharp/fsharp