Number cast fix

Number(null) should return 0, according to AS
Make PSConverter.ConvertToDouble return NaN for undefined
Make `String(null)` generate `"null"`

This behavior was missing for null constants
Standardize on the DISABLE_AS3_NULL_STRINGS define

This define now wraps all the special case handling of null getting
the string value of "null" in ActionScript. It is enabled by default,
but is present to track all of the special cases.
Fix non-aot build errors
Added [DebuggerStepThrough] and [DebuggerHidden] attributes to various infrastructure methods in pscorlib runtime to reduce stack trace spamming.
Merge pull request #326 from playscript/ps-debugger-attribs

Added [DebuggerStepThrough] and [DebuggerHidden] attributes to various i...
Compiler - added compiler tests for conversion issues, added test() method that prints source lines
Temporarily disabled failed tests
Implemented a few Date functions.
Loader now passes mimeType from URLRequest.contentType.  If it begins with 'image/' the loaded value is treated as bitmap data.  This can be used to load images from a url (such as graph.facebook.com)
Merge commit '945e550e9e75d619802464ac77baa3b82f5d302d'
Fixed profiler to not prematurely end sessions when a milestone occurs not related to loading
PS-298 Array.indexOf doesn't compare ints and Numbers succesfully
Log screen size, OS version, etc, on Android.
Merge branch 'master' of https://github.com/playscript/playscript-mono into tooling
Minor fixes for tooling compiler extensions.