Issue a UserWarning when the egg cache directory is likely to be vulnerable to security issues per #375.

--HG--
branch : distribute
Also protect against group-writable files

--HG--
branch : distribute
Update changelog

--HG--
branch : distribute
Merge second phase of fix for #375

--HG--
branch : distribute
Merge with 0.6.46 (to include additional fix for Distribute #375)
Add support for SETUPTOOLS_DISABLE_VERSIONED_EASY_INSTALL_SCRIPT variable.
Support for old DISTRIBUTE_DISABLE_VERSIONED_EASY_INSTALL_SCRIPT variable is kept temporarily for backward compatibility.

--HG--
extra : source : eb58c3fe7c0881cbb28de1c523f083ad8e7f427d
update changelog
Add comment to capture the purpose of the environment variable
Added tag 0.7.5 for changeset dd5bbc116c53
Bumped to 0.7.6 in preparation for next release.