Added build number generation [#255].

[rsjtdrjgfuzkfg]

Build numbers are now generated from git. I'm not yet certain how portable this
solution is, though. Tested on Linux; not sure if this is compatible with
Windows and/or OSX.

It will certainly break / look terrible if the user has no git installed (we could work around this, but I think that is fine).

I'm not pushing directly, as I want somebody to test this on Windows and/or OSX first (or telling me to merge so it is not my fault if it breaks :P).

[darealshinji]

You could use 2456 as a fallback build number:

BuildNumber=`git describe --long --always --dirty --abbrev=10 2>/dev/null | echo 2456`

[rsjtdrjgfuzkfg]

If one adds a fallback, I'd prefer unknown (show that something is wrong) or 0 (equal to non-official builds) over 2456; I can add that. However, I still don't know if the whole thing will work on Windows / OSX...

[freaktechnik]

on OS X it should work fine, as that's just unix, however I'm not sure if the comparison to /dev/null would work on Windows, as that path doesn't exist.

[rsjtdrjgfuzkfg]

Hm. Probably it would work without it (as it shouldn't change the overall exit code, should it?). I personally would prefer that anyways, as it would then at least log that there has been an issue (command not found / git directory missing / ...).

[darealshinji]

Doesn't /dev/null exist in Cygwin?

[rsjtdrjgfuzkfg]

We build in msys, not in cygwin. Cygwin is not capable of building real Windows applications, any application built through it requires a cygwin runtime to be installed (which is obviously not what we want for end users). Within msys, /dev/null is available, but only for tools aware of it iirc. So this mainly depends on whether this file is evaluated with bash or something unixy, or through some M$-Make-Tool (we use Visual Studio's compilers and stuff on Windows).

[freaktechnik]

I can't get building on Windows to work, so hopefully somebody else (like @AntoineTurmel ) can test build this patch.

[freaktechnik]

Works for me on windows, though I had to add git to my mozilla-build path. Should we check for git's presence if --enable-official or --enable-nightly is set?

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