Retry ACATS
Merge commit 'c48ad00' into gcc-4.7

I did NOT try ACATS with gcc-4.7 on this merge!

Conflicts:
	examples/acats/drake-expected.txt (reverted)
Implement synchronized interface
Implement Unbounded_Synchronized_Queues and Unbounded_Priority_Queues
Add and fix some entities for tasking required by compiler
Use O_CLOEXEC if it's available, instead of setting FD_CLOEXEC after open
Fix read-write locking in Windows
Fix to eliminate zero-terminators from exception names, again
Fix examples/image.adb
Add source/fix-fcntl.h to define missing O_EXLOCK, O_SHLOCK and O_CLOEXEC as 0, and remove the implementation unit System.File_Control
Make new directory nls, and add platform-depended text encoding as System.Native_Encoding
Add overloaded System.Native_Encoding.Convert and improve System.Native_Encoding.Generic_String
Change substitutes of System.Native_Encoding
Improve indexing of System.Native_Encoding
Add System.Native_Encoding.Min_Size_In_Stream_Elements and Min_Size_In_From_Stream_Elements
Fix error handling of System.Native_Encoding in Windows
Rename type System.Native_Encoding.Error_Status to Status_Type, and remove its representation clause
Improve System.Native_Encoding in the case of an insufficient buffer
Improve System.Native_Encoding.Encoding_Streams
Fix Ada.Streams.Buffer_Storage_IO to raise End_Error