Update docs to point out the problem with range constraints for conflict links.
Merge pull request #2022 from webfactory/issue-2022

"conflict" does not work for non-trivial constraints
fixed Bitbucket's broken API
Merge pull request #2035 from xrstf/bitbucket-api-fix

fixed Bitbucket's broken API
Avoid throwing when checking for disk space, fixes #2039
Merge branch 'master' of https://github.com/composer/composer