modRuntime doesn't work with local files

Clone of #101, title and description copied from there.

Not much else to say. No errors or warnings logged, any lines like the following are seemingly just ignored:

modRuntime files("file/path/here.jar")
modRuntime fileTree(dir: "dir/path/here", include: "*.jar")

With a bit of finegling, CurseForge’s automatic Maven repo is a decent substitute when trying to add local dev mods (and probably better in the long run anyways), but this is definitely a slight annoyance and may not be avoidable for other applications. modCompile does work with files, but not with fileTree, and obviously doesn’t have the benefit of modRuntime’s runtime-only properties.

[modmuss50]

In 0.7 loom I have expanded this to allow passing in any paths. You are supposed to be able to pass in a custom configuration as well but I broke this and do plan on fixing it.

[Earthcomputer]

The workaround for JIJ’ing jars built from other source sets (e.g. an API jar) turned out to be quite simple:

task remapApiJar(type: RemapJarTask, dependsOn: project.apiJar) {
	input = apiJar.archiveFile
	classifier = 'api'
	addNestedDependencies = false
}
remapJar.dependsOn remapApiJar

repositories {
	// ...
	flatDir {
		dirs file(remapApiJar.archivePath).parentFile
	}
}

dependencies {
	include name: file(remapApiJar.archivePath).name.with { it.endsWith('.jar') ? it.substring(0, it.length() - 4) : it }
}

Thanks to mbfrog for his workaround, didn’t know flatDir repos existed until now.