util.startup: Handle missing nparams field from debug info (not present in 5.1)

core.modulemanager: Fix error if installer path missing Happens if run outside prosody. Noticed because because the storage tests fail.

util.startup: Include arguments in function string representation Improves usability of the console when digging around the internals. No specific rationale for the function<file:line>(args) format, it looked best of the variants I tried.

util.startup: Retrieve less data for function string representation debug.getinfo(f) collects more info than what is needed here.

core.moduleapi: Return resource path from module:get_directory() (API BC) :get_directory has so far returned the base directory of the current module source code. This has worked well so far to load resources which tend to be included in the same directory, but with the plugin installer using LuaRocks, extra resources (e.g. templates and other assets) these are saved in a completely different directory. In be73df6765b9 core.modulemanager gained some code for finding that directory and saving it in module.resource_path but now the question is how this should be reflected in the API. A survey of community modules suggest the vast majority use the :get_directory method for locating templates and other assets, rather than the code (which would use module:require instead). Therefore this commit changes :get_directory to return the resource_path when available. This should work for most modules.

core.modulemanager: Add compat for LuaRocks 2.x

core.moduleapi: Use resource path for :load_resource()

core.modulemanager: Locate resources of LuaRocks-installed modules Extra non-code files included with a `copy_directories` directive in a LuaRocks manifest will be copied into a per-module and per-version directory under /lib/luarocks/ and all this is there to dig that out so it can be used in e.g. moduleapi :load_resource().

util.startup: Save the path used by the installer to prosody.paths Makes it easier for other parts of the code to use this for things, such as determining whether a certain module is from this path or from elsewhere.

Merge 0.11->trunk