Do not shadow submodules

using object that have the same name as submodules as the weird effect
of makeing `import pip.commands.<something> as <anothername>` fail with
a key error. This fixes it by renamin commands as command_dict and fixin
a few imports to accomodate.

Related to #2149
RELEASE notes
install: "Cleaning up..." msg: info => debug

This message isn't particularly useful to an end user and clutters the
output IMHO.
"Running setup.py...egg_info" log: INFO => DEBUG

Change log level of `"Running setup.py (path:%s) egg_info"` log messages
from INFO to DEBUG. The average user does not know or care that pip is
running `python setup.py egg_info`, unless things are broken, IMHO.

See: GH-1070
install: Make some warnings DEBUG rather than INFO

* `warning: no previously-included files matching`
* `warning: no files found matching`

See: GH-1070
Merge pull request #2175 from msabramo/make_cleaning_up_a_debug_msg

install: "Cleaning up..." msg: info => debug
Merge pull request #2177 from msabramo/egg_info_log_debug_instead_of_info

"Running setup.py...egg_info" log: INFO => DEBUG
Merge pull request #2178 from msabramo/pip_install_make_some_warnings_debug

install: Make some warnings DEBUG rather than INFO
Update the change log
update submodules after checkout
Merge pull request #2172 from Carreau/shadow-submodule

Shadow submodule
Revert "RELEASE notes"

This reverts commit 279569a164910f0ae8f202c724808d631e241ceb.
Merge pull request #2181 from dacjames/develop

update submodules after checkout
Fix for latest setuptools
Merge pull request #2182 from dstufft/fix-latest-setuptools

Fix for latest setuptools
Vendor Packaging
Upgrade setuptools
Implement PEP 440
Merge pull request #1894 from dstufft/use-packaging

PEP 440 Version and Specifiers
Change "Downloading/unpacking" to "Collecting"

"Downloading/unpacking" was misleading and confusing, especially when
the package is never found, as nothing was ever downloaded or unpacked
in this case.

The word "collecting" seems general enough to be accurate and it goes
well with the fact that later on pip will say, "Installing collected
packages".

Fixes: GH-376