Clarify requirement specifier format

If you use single or double quotes in a `requirements.txt` file, pip exits with an error. This change clarifies that single or double quotes should only be used in the shell.
req: Support --no-use-wheel flag in requirements.txt

Default from pip 1.6 will be to always use wheels, so the --use-wheels
in requirements.txt is now deprecated. However, the --no-use-wheels
is introduced to be able to disable wheel usage via requirements.txt.
Document the --no-use-wheel in requirements.txt
query installed requirements for extras

fixes issue where egg_info('requires.txt') does not exist
for packages installed from wheels.
Merge pull request #1896 from dstufft/extras_after_wheel

Query installed requirements for extras
Merge pull request #1859 from nailor/support-no-use-wheel

req: Support --no-use-wheel flag in requirements.txt
Add #1859 to the changelog
Merge pull request #1848 from daviewales/clarify-documentation

Clarify requirement specifier format
Use a regex to avoid hard coding version branches
Merge pull request #1906 from dstufft/ugh

Use a regex to avoid hard coding version branches
Run the unit tests before the integration tests
Timeout the test runs
Merge pull request #1908 from dstufft/ugh

Run the unit tests before the integration tests
Show coverage information for tests
Merge pull request #1909 from dstufft/ugh

Show coverage information for tests
Use diff-cover to show the change in coverage
Remove some noise in the output
Use the correct parameter name
Protect against coverage files not existing
Merge pull request #1910 from dstufft/ugh

Use diff-cover to show the change in coverage