cpdb-backend-cups 2.0b7

In the seventh beta release for cpdb-backend-cups 2.0.0 the development was mostly led by Biswadeep Purkayastha, GSoC contributor on CPDB support for LibreOffice, and his mentor Michael Weghorn, LibreOffice developer. Some bugs got fixed and support for CUPS' printer instances added.

• Add support for CUPS printer instances
  Don't just always use the cups_dest_t's name for the printer name, but also take it's instance member into account and if present, append that for the name used for the CPDB printer name, separated by a slash character (Pull request #34).
• Always query current CUPS default printer
  When asked for the default printer, always query and return the current CUPS default printer instead of whatever was the default last time this was done, to take into account that the CUPS default printer can change while the backend is running (Pull request #33).
• Pass correct parameters to cupsStartDestDocument()
  Now job title and job attributes (options) are correctly passed on (Pull request #36).
• Use NULL Instead of "NA" if there's no default printer
  NULL makes clear that there's no default printer, while "NA" could even be the name of an actual printer, so use the former instead of the latter if no default printer could be determined (Pull request #35).
• Use g_strdup instead of cpdbGetStringCopy
  GLib's g_strdup already provides the same functionality as cpdbGetStringCopy from cpdb-libs, so use the former instead of relying on a custom CPDB implementation (Pull request #32).