Add support for debug builds (-g flag)

[gsingh93]

I think there should be a way to optionally pass the -g flag to rustc. My specific use case is that I need a binary with debug information for use with kcov.

[steveklabnik]

The intention is that normal builds will include -g, and release builds will not, so this won't be needed specifically. That said, rustc's debugging support is kinda broken for certain things at the moment, so this is temporarily disabled until then.

[alan-andrade]

That's good to know, I needed the same "feature".

[alexcrichton]

This is now implemented! See the profile section of http://crates.io/manifest.html for more information.

I should also note that this is now the default for regular/test profiles, you'll just have to opt-in to debuginfo for release builds.

[pratz]

This is awesome
+1