[WIP] finalize using freeProblem

to fix #7 . I'm getting the following:

```bash
$ julia hs015_tuner.jl
[...]
The fastest locally optimal solution was found by Solve 39
Tuner non-default option settings for this solve are:
algorithm:            2
bar_murule:           1

Summary Statistics
---------------------------------------------------------------------------
                                            Percent   Average     Average
    Option Name          Value      #Runs   Optimal  #FuncEvals     Time
--------------------  ----------  --------  -------  ----------  ----------
  bar_directinterval           0        24   100.00        14.2       0.001
  bar_directinterval           1        24   100.00        12.3       0.001
  bar_directinterval          10        24   100.00        12.2       0.000
--------------------  ----------  --------  -------  ----------  ----------
          bar_murule           1        12   100.00        12.0       0.001
          bar_murule           2        12   100.00        12.7       0.000
          bar_murule           3        12   100.00        13.3       0.000
          bar_murule           4        12   100.00        13.3       0.000
          bar_murule           5        12   100.00        14.7       0.000
          bar_murule           6        12   100.00        11.7       0.000
--------------------  ----------  --------  -------  ----------  ----------
               pivot    1.00e-08        37   100.00        12.8       0.001
               pivot    1.00e-14        37   100.00        12.8       0.000
--------------------  ----------  --------  -------  ----------  ----------
           algorithm           1        36   100.00        16.1       0.001
           algorithm           2        36   100.00         9.8       0.000
           algorithm           3         2   100.00         7.0       0.002
---------------------------------------------------------------------------

===============================================================================
KNITRO.jl: freeing problem
KNITRO: calling freecontext on Ptr{Void} @0x0000000112996000
C_NULL (for reference): Ptr{Void} @0x0000000000000000

signal (11): Segmentation fault: 11
ktr_magic_check at /Users/yeesian/knitro-9.0.1-z/lib/libknitro.dylib (unknown line)
KTR_free at /Users/yeesian/knitro-9.0.1-z/lib/libknitro.dylib (unknown line)
freecontext at /Users/yeesian/.julia/v0.3/KNITRO/src/ktr_functions.jl:31
freeProblem at /Users/yeesian/.julia/v0.3/KNITRO/src/KNITRO.jl:69
jl_apply at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/gf.c:1416
jl_apply at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/./julia.h:1174
run_finalizers at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/gc.c:318
uv_atexit_hook at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/init.c:447
_start at /Applications/Julia-0.3.0.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
_start at /Applications/Julia-0.3.0.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
jl_apply at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/./julia.h:980
true_main at /Applications/Julia-0.3.0.app/Contents/Resources/julia/bin/julia (unknown line)
julia_trampoline at /Users/vagrant/tmp/julia-packaging/osx10.7+/julia-release-0.3/src/init.c:1007
Segmentation fault: 11
```