cups-browsed 2.0rc2

Some final, important bug fixes before the release: 100% CPU after failed printer access, broken print-quality-default attribute.

• Fixed cups-browsed getting stuck in busy loop
  When the function create_queue() fails to create a local print queue and the failure is not intermittent, it sets a global variable to stop the main thread's loop for updating local queues. With the variable not reset no queue updates happened ever again and cups-browsed fell into a busy loop taking up to 100% CPU. We have solved this by doing away with the variable and simply mark these printers as disappeared (Ubuntu bug #2018504).
• Do not record *-default IPP attributes of local CUPS queues
  Many of the *-default IPP attributes represent properties already covered by the PPD option defaults which we also record. In addition, there is also print-quality-default where IPP reports draft, normal, and high settings while CUPS only accepts 3, 4, and 5, and on everything else it sets print-quality-default=0 which is invalid and jobs do not get printed. So we stop saving and loading these attributes.
• Build system: Removed unnecessary lines in Makefile.am
  Removed the TESTdir and TEST_SCRIPTS entries in Makefile.am. They are not needed and let make install try to install run-tests.sh in the source directory, where it already is, causing an error.
• run-tests.sh: Use pkgconfig instead of deprecated cups-config (Pull request #9).