Code review comment for lp:~dobey/libubuntuone/srcdir-signing

OK, not using $(srcdir)/ in the dependencies declarations seems to work, so I removed the instances where it was used. I also removed the |sed portion of the check rule, since we're not using it yet, but I figured it might be useful to perhaps use the key id in the future. It's easy to add back though and not calling sed saves us a microsecond of build time.

I made AssemblyInfo.cs depend on mono.snk because we're replacing a string with the path to it. If the source file doesn't exist, it should fail there, rather than wasting time generating the file and then trying to compile all the csharp files into the dll, only to have it fail later. Earlier failures are better.

As for depending on Makefile, anything which generates a file via automatic inclusion in another rule, like we do here, it should depend on Makefile so that the file gets rebuilt if Makefile changes. For instance, if any variables we're inserting into the file with sed like this, have changed, the file needs to be regenerated with the new values.