qca 2.1.0, with Qt plugins

Overhaul of `qca` formula to address v2.1.0 changes since 2010's v2.0.3 release. See [changes](http://quickgit.kde.org/?p=qca.git&a=blobdiff&h=c7bad342392e79f9a3a59a042eafa40ccfb3cd2f&hp=000eb314df04d71bed486a784a36096abaf0cb8f&hb=f1b2a891c376445f3e880c2ed7edbaf2b8a2647a&f=README).

Includes new CMake build setup, which handles building all QCA plugins, whose source is now internal to overall project. Since QCA really needs at least one plugin to be useful, the `qca-ossl` (OpenSSL-based) plugin is ON by default.

The output now defaults to `qca.framework` which is inline with other Qt-related libs, e.g. `qwt`, `qwtpolar`, etc.

API docs generation is optional, as current online docs are [still outdated](http://delta.affinix.com/docs/qca/). No option to build examples is included, as the same full example code is embedded in API docs.
Make this a variable instead of a function.