update debug() to use IPython-enabled pdb if available
update debug() to use IPython-enabled pdb if available

- the debugger now starts in the caller's frame - pressing 'n' is no
  more necessary

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