Removed the mention of "package index options" in the docs, because they don't all fit that category anymore. Not even --no-binary and --only-binary do; they're "install options".
`pip download` has the same functionality as `pip install --download`,
and the behavior of `pip install --download` is preserved with a deprecation
warning. `pip install --download` will be removed in pip version 10.
This adds constraints files. Like requirements files constraints files
control what version of a package is installed, but unlike
requirements files this doesn't itself choose to install the package.
This allows things that aren't explicitly desired to be constrained if
and only if they are installed.
Wheel cache lookups become more complex when we wish to allow binary
blacklisting. Rather than passing more parameters around, replace
cache_root with wheel_cache, and create a wheel cache in all the
relevant command entry points.
* Deprecates the --download-cache option & removes the download
cache code.
* Removes the in memory page cache on the index
* Uses CacheControl to cache all cacheable HTTP requests to the
filesystem.
* Properly handles CacheControl headers for unconditional
caching.
* Will use ETag and Last-Modified headers to attempt to do a
conditional HTTP request to speed up cache misses and turn
them into cache hits.
* Removes some concurrency unsafe code in the download cache
accesses.
* Uses a Cache-Control request header to limit the maximum
length of time a cache is valid for.
* Adds pip.appdirs to handle platform specific application
directories such as cache, config, data, etc.
Add a 'retry' option which allows to configure how many
retries pip should make before giving up on HTTP request.
When the retries count is specified by user, its value is
passed to HTTPAdapter from requests which handles all
the underlying operations.
Using sys.exc_info()[1] is a hack that was used to use a shared
source approach to Python 3.x support that also included versions
of Python that didn't include the except ... as exc: construction.
Pip no longer supports any of these versions of Python so we can
remove it.
