Clean up filt()

Fixes the special case for FIR filters, which AFAICT was previously
unreachable. However, it will often be faster to perform FIR filtering
by FFT, and in the future we might want to do that.

Requires that coefficients are numbers or AbstractVectors and that x is
an AbstractVector, since I think the previous behavior would have
produced unexpected results for anything else. I've punted on promoting
types for now, since I'm not sure what best practice is, although I'm
happy to learn.

Also adds tests.
Search $LDFLAGS directories before the system default directories, in the case of overrides
Add in a script to filter out duplicate libraries; only take the first found one
Merge pull request #3186 from staticfloat/master

Search $LDFLAGS for SuiteSparse before system libraries
Update Gedit file after review in Gnome's bug tracker
Merge pull request #3187 from waldir/master

Update Gedit syntax highlighting file after review in Gnome's bug tracker
Merge pull request #3183 from simonster/filt

Clean up filt()
add generic set_source
generalize arguments to diagonal() and aspect_ratio()
Merge branch 'master' of github.com:JuliaLang/julia
fix typo
add back count(pred,itr). closes #3180
some doc updates
retry rehash() if Dict is changed during the process. should fix #3181 for real this time.
Fixed indenting in tm bundle
Merge pull request #3193 from malmaud/tmfix

Fixed indenting in tm bundle
Merge branch 'master' into my_mac_use