extensions: include current version in "invalid version" message
It is "not so rare" for the mercurial version to be badly detected at build
time. In such case, version check for extensions gets confused.
To help pinpoint the error, we now include the Mercurial's version number in
the error message.
node = <module 'mercurial.node' from '?'>
errorproxy = <unloaded module 'error'>
errorproxy.__doc__ = 'Mercurial exceptions. This ...'
errorproxy.__name__ = 'mercurial.error'
errorproxy.__dict__['__name__'] = 'mercurial.error'
errorproxy = <proxied module 'error'>
os = <unloaded module 'os'>
os.system = <built-in function system>
os = <module 'os' from '?'>
procutil = <unloaded module 'procutil'>
procutil.system = <function system at 0x?>
procutil = <module 'mercurial.utils.procutil' from '?'>
procutil.system = <function system at 0x?>
hgweb = <unloaded module 'hgweb'>
hgweb_mod = <unloaded module 'hgweb_mod'>
hgweb = <module 'mercurial.hgweb' from '?'>
fred = <unloaded module 're'>
remod = <unloaded module 're'>
re = <unloaded module 'sys'>
fred = <unloaded module 're'>
fred.sub = <function sub at 0x?>
fred = <proxied module 're'>
remod = <module 're' from '?'>
re = <unloaded module 'sys'>
re.stderr = <open file '<whatever>', mode 'w' at 0x?>
re = <proxied module 'sys'>
contextlib = <unloaded module 'contextlib'>
contextlib.unknownattr = ImportError: cannot import name unknownattr
__import__('contextlib', ..., ['unknownattr']) = <module 'contextlib' from '?'>
hasattr(contextlibimp, 'unknownattr') = False