convert: fixed python2.3 incompatibility in bzr source (generator expression)

Improve error handling in osutil.c 1) In posix part set error when path is too long so instead of SystemError: error returned without exception set it will raise ValueError: path too long 2) In Win32 part replace generic PyErr_SetExcFromWindowsErrWithFilename by PyErr_SetFromWindowsErrWithFilename The exception returned is WinError(based on OSError) and some rudimentary errno translation is performed from Windows error range to errno module friendly range so errors like ENOENT can be handled via symbolic constant and consistently between Win32 and Posix.

`source` doesn't work for some /bin/sh, use `.` instead

fix conflicting variables when no native osutil is available thanks weijun for the bug report and patch, fix issue1309

osutil: implementation for Win32 Use information provided by FindFile... Win32 calls to generate stat information without lstat call per file. rwx bits in st_mode are ignored as they are not stored in Win32 fs and Mercurial does not use them Unicode path / path names over _MAX_PATH are intentionally not supported.

convert: improve convert_source documentation

get-with-headers: fix stream modes under Windows

convert: add bzr source

merge with crew-stable

i18n, churn: mark string for translation