Create gslerrno for multimin functions
This commit creates the gslerrno variable within various multidimensional minimizer functions where this value was not previously being created but was being checked for a value.
Apply changes from issue #51 for precompilations and warnings
This commit applies the updates from issue #51 provided by @yuyichao for enabling pre-compilation and removing warnings for method redefinition, but makes all code changes to non-underscored files. The original order of loading files within __FILELIST.jl and GSL.jl is maintained by making edits to the include commands within __FILELIST.jl and removing entries from GSL.jl. Tests of pre-compilation and execution of runtests.jl were performed for Julia 0.4.3 and the current Julia 0.5.0-dev nightly build.