osutil: consider WindowsError's behaviour to support python 2.4 on Windows

This change treat the ESRCH error as ENOENT like WindowsError class
does in python 2.5 or later. Without this change, some try..execpt
code which expects errno is ENOENT may fail. Actually hg command does
not work with python 2.4 on Windows.

CreateFile() will fail with error code ESRCH
when parent directory of specified path is not exist,
or ENOENT when parent directory exist but file is not exist.
Two errors are same in the mean of "file is not exist".
So WindowsError class treats error code ESRCH as ENOENT
in python 2.5 or later, but python 2.4 does not.

Actual results with python 2.4:
>>> errno.ENOENT
2
>>> errno.ESRCH
3
>>> WindowsError(3, 'msg').errno
3
>>> WindowsError(3, 'msg').args
(3, 'msg')

And with python 2.5 (or later):
>>> errno.ENOENT
2
>>> errno.ESRCH
3
>>> WindowsError(3, 'msg').errno
2
>>> WindowsError(3, 'msg').args
(3, 'msg')

Note that there is no need to fix osutil.c because it never be used
with python 2.4.

mercurial/pure/osutil.py

@@ -59,6 +59,7 @@ if os.name != 'nt':
     posixfile = open
 else:
     import ctypes, msvcrt
+    from errno import ESRCH, ENOENT
 
     _kernel32 = ctypes.windll.kernel32
 
@@ -98,7 +99,14 @@ else:
 
     def _raiseioerror(name):
         err = ctypes.WinError()
-        raise IOError(err.errno, '%s: %s' % (name, err.strerror))
+        # For python 2.4, treat ESRCH as ENOENT like WindowsError does
+        # in python 2.5 or later.
+        # py24:           WindowsError(3, '').errno => 3
+        # py25 or later:  WindowsError(3, '').errno => 2
+        errno = err.errno
+        if errno == ESRCH:
+            errno = ENOENT
+        raise IOError(errno, '%s: %s' % (name, err.strerror))
 
     class posixfile(object):
         '''a file object aiming for POSIX-like semantics