From hgweb, calling archival.zipit fails with the error message
"Illegal seek". This happens because sys.stdout.tell() throws an
exception:
Traceback (most recent call last):
File "/usr/lib/python2.4/site-packages/mercurial/archival.py", line 99, in addfile
self.z.writestr(i, data)
File "/usr/lib/python2.4/zipfile.py", line 468, in writestr
zinfo.header_offset = self.fp.tell() # Start of header bytes
Checking whether hasattr(dest, 'tell') is insufficient, because
sys.stdout has a tell() method; you just can't call it.
This patch instead determines whether a fileobj is tellable by trying
to tell(), wrapping the fileobj if an exception is generated.
