Boost 1.56 with boost-python

[tdsmith]

This PR will upgrade Boost to 1.56 (changes from #31428) and split Boost.Python into a new boost-python formula.

Continuation of #30957; accidentally deleted my remote git branch, oops.

Deployment plan:

• pull this PR, updating existing bottles
• pull-request ledger with a bumped revision and pull against 1.56
• pull homebrew/homebrew-science#1149

As discussed, users will encounter upgrade failures of the form:

==> Upgrading ledger
Error: /usr/local/opt/boost-python not present or broken
Please reinstall boost-python. Sorry :(

The workaround is brew install boost-python && brew upgrade.

[tdsmith]

Hey @MikeMcQuaid, pull --bottle failed with this message:

darkside:local tim$ brew pull https://github.com/Homebrew/homebrew/pull/32704 --bottle
curl: (22) The requested URL returned error: 404 Not Found
Error: Failure while executing: /usr/bin/curl -f#LA Homebrew\ 0.9.5\ (Ruby\ 2.0.0-481;\ Mac\ OS\ X\ 10.9.5) https://github.com/BrewTestBot/homebrew/compare/homebrew:master...pr-32704.patch -o /Library/Caches/Homebrew/homebrew:master...pr-32704.patch

but the bottles were built successfully and pushed to sourceforge and manually updating the hashes in the formula (from here) seems to work. Does anything need to happen to keep the built bottles around on sourceforge?

[tdsmith]

Nevermind; helps if you wait for the bottles to upload.

[tdsmith]

Completed at 5057268.