better detection of docs theme
- if installing directly from a wheel, fail if it has an invalid name or is unsupported
- when walking links, skip invalid wheel filenames, don't crash
unsuppress --log-file
add 'distribute' to default skip list for installed dists
add warning to --egg option, see https://github.com/pypa/pip/issues/1320
Merge pull request #1321 from qwcode/skip_distribute

add 'distribute' to default skip list for installed dists
Merge pull request #1316 from qwcode/log_file

unsuppress the help for --log-file
Merge pull request #1315 from qwcode/check_wheel_support

don't crash when crawling invalid wheels;  if installing directly, fail if invalid or unsupported