IN TMinuit::mnparm, replace call to mnfree(1) by mnfree(-k).

mnfree(1) frees only the last fixed parameters. The change takes care
of multiple fixed parameters.
Also small change in print format for parameters between boundaries.
Thanks to Marco van Leeuwen.


git-svn-id: http://root.cern.ch/svn/root/trunk@2828 27541ba8-7e3a-0410-8455-c3a389f83636