Support pager on Windows

Windows does not support pipe|fork, but we can simulate by creating
the pager as a child process, redirecting stdout/in/err appropriately
and then waiting for the child process to terminate after we are
done executing the repo command.

Change-Id: I5dd2bdeb4095e4d93bc678802e53c6d4eda0235b

main.py

@@ -55,7 +55,7 @@ from error import NoSuchProjectError
 from error import RepoChangedException
 import gitc_utils
 from manifest_xml import GitcManifest, XmlManifest
-from pager import RunPager
+from pager import RunPager, TerminatePager
 from wrapper import WrapperPath, Wrapper
 
 from subcmds import all_commands
@@ -542,6 +542,7 @@ def _Main(argv):
       print('fatal: %s' % e, file=sys.stderr)
       result = 128
 
+  TerminatePager()
   sys.exit(result)
 
 if __name__ == '__main__':