file descriptors returned by os.pipe() are from the same pool as file.fileno()
added dup and dup2
further improvements for dup, dup2, pipe, open

changed to make it .net 3.5 compatible
pipe related code is wrapped in FEATURE_PROCESS
dup2 and open allocate lowest available fd
added os.closerange
os.open can open 'nul' file on windows
os.close closes underlying stream only if last fd is closed
added fd_test.py
Rename decorators -> decorator_list in ast.FunctionDef to make it consistent with cpython ast
Catch failures when closing streams.
Merge branch 'tinker-with-file' into ipy-2.7-maint
Merge remote-tracking branch 'lck/ipy-2.7-maint' into ipy-2.7-maint