package nsis: enable native 64-bit build and remove multi-lib requirements from docs
Makefile: add error messages for undefined package or url
Makefile: fix indentation of missing url check
Makefile: fix indentation of missing url check
Fix gtksourceview update script

Fix gtksourceview update script. It could consider .tar.gz suffixes
part of the version number.

Problem reported by Niels Kristian Bech Jensen <nkbj1970@hotmail.com>.
Package fltk: update download URL
Update package gdal
Update package imagemagick
Update package netcdf
Update package netpbm
Update package ocaml-flexdll
Update package pixman
Merge pull request #187 from uklauer/updates

Update some packages