Updates to allow F# to build without .Net 2.0 to being present on Mono
Removed FSharp.Core from lib/bootstrap/2.0
Moved all required bootstrap files from lib/bootstrap/2.0 to 4.0 folder
Updated build scripts to reflect the above change
Added conditions to the build script to only build a version 2.0 of FSharp.Core if
that version of mscorlib is available.

Mono plans to remove .Net2.0 and 3.5 assemblies in the next version.
Added mscorlib assembly redirects for all .Net 2.0  compiled files
Copy and add FsSrGen from F# PowerPack
Replase fssrgen.exe
Add FSharp.SRGen.Build.Tasks from F# power pack and build for .NET 4.0
replace LKG with latest FsLexYacc.Build.Tasks.dll
simplify paths to LKG
simplify paths to LKG
remove use of FSharp.Core 4.3.1.0
update binding redirects for fslex and fsyacc
update fslex/fsyacc
fix makefile problem
Merge pull request #350 from 7sharp9/net20fix

Updates to allow F# to build without .Net 2.0 to being present on Mono