Ubuntu trusty has a bug in curl when using NTLM credentials in a proxy, dereferencing a null pointer and causing segmentation faults. Use a custom-patched version of libcurl that avoids this issue.
Some tests of ours require to be running against an SSH server. Currently, we simply run against the SSH server provided and started by Travis itself. As our Linux tests run in a sudo-less environment, we have no control over its configuration and startup/shutdown procedure. While this has been no problem until now, it will become a problem as soon as we migrate over to newer Precise images, as the SSH server does not have any host keys set up. Luckily, we can simply set up our own unpriviledged SSH server. This has the benefit of us being able to modify its configuration even in a sudo-less environment. This commit sets up the unpriviledged SSH server on port 2222.
The formulae provided by the homebrew/dupes tap are deprecated since at least April 4, 2017, with formulae having been migrated to homebrew/core. Replace the deprecated reference to "homebrew/dupes/zlib" with only "zlib".
Download mingw-w64 into our build directory and execute it there, don't try to overwrite the system's mingw.
When running a Coverity build, we have to provide an authentication token in order to proof that we are actually allowed to run analysis in the name of a certain project. As this token should be secret, it is only set on the main repository, so when we were requested to run the Coverity script on another repository we do error out. But in fact we do also error out if the Coverity analysis should _not_ be run if there is no authentication token provided. Fix the issue by only checking for the authentication token after determining if analysis is indeed requested.
We used to only execute Coverity analysis on the 'development' branch before commit 998f001 (Refine build limitation, 2014-01-15), which refined Coverity build limitations. While we do not really use the 'development' branch anymore, it does still make sense to only analyze a single branch, as otherwise Coverity might get confused. Re-establish the restriction such that we only analyze libgit2's 'master' branch. Also fix the message announcing why we do not actually analyze a certain build.