More flexible build for Lurch4Adium

[shtrom]

Make the build more flexible by allowing to override the Makefile variables.

This was needed to support making an Adium plugin in shtrom/Lurch4Adium.

Also fix another few things.

[anthraxx]

why does it remove github submodule URLs and changes the .gitmodules to use parent directories?

[shtrom]

Ha, this was to be more flexible: git will resolve submodules based on the URL of the superproject. If lurch is cloned from github/gkdr/lurch, all submodules will be cloned from there (i.e., github/gkdr/lurch/../SUBMODULE).

Making this change made it easier for me to work on the whole codebase in clones from my own GitHub repo without having to fiddle too much.

I think it's generally a sane thing to do, but I'm happy to revert to hard-coded URL if desired.

[gkdr]

Finally getting around to doing a few things.
Thanks for your porting effort and glad it was not that hard to do. Unfortunately, this doesn't quite work.
You forgot the -fPIC compile flag for lurch itself, and to call pkg-config for sqlite3 and mxml.
After adding those back and getting rid of compilation and linking errors, I still get:

(22:05:22) plugins: /home/riba/.purple/plugins/lurch.so is not usable because the 'purple_init_plugin' symbol could not be found.  Does the plugin call the PURPLE_INIT_PLUGIN() macro?

I can't see that it's not being called, so I'm not quite sure what's going on. For now I'm gonna go to bed though.

[EionRobb]

'purple_init_plugin' symbol could not be found can happen if PURPLE_PLUGINS is not #defined or -Dd

[gkdr]

There was an underscore missing! After also changing the PLUGIN_CPPFLAGS var from -DPURPLEPLUGINS to -DPURPLE_PLUGINS, it compiles and loads fine. Thanks, @EionRobb!

[shtrom]

Ah. Do you want me to fix the PR, or are you happy to just add a commit on top?

[gkdr]

It's fine, I already fixed it in the local branch I pulled this PR into, and merged everything into the dev branch. Should show up as merged once I merge it into master.