bin/duneproject: Fix, modernize and document check for existing modules

Fixes:

• Use unambiguous truth values (Closes: #134 (closed))
• When checking with pkg-config, look for the dependency rather than the last module from the list of found modules

Modernizations:

• Scope variables
• Use a simple if rather than a loop to check for presence of a depency in list of existing modules
• Make sure the function does not depend on the status of the -e option, or whether it is called from within the condition of an if or a || or &&.

Documentation:

• Document calling convention for the function and assumptions on the parameters.