pdftotext only called if present in system, minor edit

David and Raul had both reported that because 'pdftotext' wasn't available
on their system, the project failed (even though the PDF was built!). So
with this commit, we first check if the system has 'pdftotext' and call it
only if its is available.

Some minor edits were made, building upon Boud's previous commit.

0 files changed, 0 insertions, 0 deletions