the build script has to be executed by bash

The build.sh script is not POSIX-compliant so it shouldn't rely on /bin/sh being Bash, but it should explicitly ask to be executed by Bash.
PDF is now building on OSs with case sensitive name files.
Merge pull request #3043 from jerrinot/docufixes

PDF is now building on OSs with case sensitive filenames.
Full spell checking performed.