Fix the registry checking on mono to avoid unnecessary exceptions being thrown. Each time there is a check for the location of the default compiler the registry is first checked.  On mono these steps will always fail as the registry location is readonly by default and the pinvoke call always results in a failure as Advapi32.dll.dll does not exist.  A similar fix was committed to the F# addin code which was using a derivative of this piece of code.
Fix the registry checking on mono to avoid unnecessary exceptions being thrown.
Each time there is a check for the location of the default compiler the registry
is first checked.  On mono these steps will always fail as the registry
location is readonly by default and the pinvoke call always results in a failure
as Advapi32.dll.dll does not exist.  A similar fix was committed to the F# addin code
which was using a derivative of this piece of code.

sergey-tihon/FSharp.Compiler.Service,rojepp/FSharp.Compiler.Service,rneatherway/FSharp.Compiler.Service,0x53A/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,sergey-tihon/FSharp.Compiler.Service,forki/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,matthid/FSharp.Compiler.Service,alfonsogarciacaro/FSharp.Compiler.Service,jeroldhaas/FSharp.Compiler.Service,alfonsogarciacaro/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,matthid/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,yever/FSharp.Compiler.Service,rojepp/FSharp.Compiler.Service,yever/FSharp.Compiler.Service,0x53A/FSharp.Compiler.Service,forki/FSharp.Compiler.Service,matthid/FSharp.Compiler.Service,BillHally/FSharp.Compiler.Service,alfonsogarciacaro/FSharp.Compiler.Service,rneatherway/FSharp.Compiler.Service,vasily-kirichenko/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service,jeroldhaas/FSharp.Compiler.Service,BillHally/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,vasily-kirichenko/FSharp.Compiler.Service,vasily-kirichenko/FSharp.Compiler.Service,0x53A/FSharp.Compiler.Service,rojepp/FSharp.Compiler.Service,sergey-tihon/FSharp.Compiler.Service,forki/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service