Make fastwriter a soft dependency

[Matthias Vogelgesang]

To compile pcitool one is either required to have fastwriter installed or have to disable the commandline tool. fastwriter comes with its own bag of dependencies that need to be installed. All this for a use case we do not have often. I'd suggest to make fastwriter a soft dependency, i.e. fallback to a simpler way of writing in case it cannot be found at configure time.

[Suren A. Chilingaryan]

Thats will require significant changes in the grabbing logic within pcitool binary (I kind of expect that writing takes no time as fastwriter handles buffering). On the other hand fastwriter is SIGNIFICANTLY faster compared to writing with standard write and only requires xfsprogs (and even this requirement is optional).

In general, I am thinking about redesign which will reduce number of memcopies. When/If? this finally will happen I'll think about making fastwriter optional.

[Suren A. Chilingaryan]

I am just finishing a obs repository with RPMs for all camera related stuff. I guess it should relax the problem. Therefore, I am closing it.
​https://build.opensuse.org/project/show/home:csa7fff:alps