Add support for compiling against .NET 4.5 in VS2010.
By default, tune GC settings in JSILc to use sustained low latency mode & server GC.
Manually trigger full background collections after assembly load, analysis and translation phases complete.
Collectively these GC changes reduce time spent in GC during a corlib compile from ~50% to ~11%.
Some minor heap size/GC pressure optimizations
Introduce ImmutableArrayPool to reduce GC pressure by carving small temporary arrays out of larger ones
Use ToList in some places instead of ToArray to reduce GC pressure
Clean up a few resharper warnings
Fix .NET 4.0 build