mod_mam_archive should define resolve_relative_path function

[GoogleCodeExporter]

When mod_mam_archive is active and a client requests history, there is 
currently the following stack trace:

error   Traceback[c2s]: 
.../prosody/modules/mod_mam_archive/mod_mam_archive.lua:145: attempt to call 
global 'resolve_relative_path' (a nil value)
stack traceback:
        .../prosody/modules/mod_mam_archive/mod_mam_archive.lua:145: in function 'get_db'
        .../prosody/modules/mod_mam_archive/mod_mam_archive.lua:191: in function '?'

The fix is easy, just add the following line to the requires logic section:

local resolve_relative_path = require 
"core.configmanager".resolve_relative_path;

Original issue reported on code.google.com by vstak...@gmail.com on 14 Aug 2014 at 7:02

[GoogleCodeExporter]

Also I've found an error with times handling.

Here is the patch suggested:
https://gist.github.com/vstakhov/306ea813a38021dcf3d4

Original comment by vstak...@gmail.com on 15 Aug 2014 at 3:01