[pvr.wmc] use safe format arg to snprintf

Prior to this commit, the wmc PVR addon failed to build if
-Werror=format-security was used. The compiler could not examine the
contents of the results array.

Adjust the snprintf calls so that the format string is a string literal.

Fedora recently enabled this compiler option in their RPM builds, so
this fixes the build on Fedora 21.
[pvr.wmc] bump version to 2.96
Merge pull request #296 from ktdreyer/pvr-wmc-format-string

[pvr.wmc] use safe format arg to snprintf