update import_file() to use full package paths for sfepy modules
update import_file() to use full package paths for sfepy modules

- prevents name clashes for different fields.py files

rc/sfepy,BubuLK/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,RexFuzzle/sfepy,rc/sfepy,vlukes/sfepy,lokik/sfepy,sfepy/sfepy,lokik/sfepy,sfepy/sfepy,sfepy/sfepy,RexFuzzle/sfepy,lokik/sfepy,lokik/sfepy,vlukes/sfepy,rc/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,vlukes/sfepy