Multiple changes

- Updated the build system:
  - Fixed a problem in the common external library detection macro.
  - Reimplemented EGL detection.
- Updated/fixed the devel/testing implementation of EGL:
  - Renamed eglGetConfig to eglGetConfigs.
  - Added support for new config attributes.
  - Added the eglWaitGL function.
- Minor update in an standalone example.
- Minor updates in an EGLplus example.
- Updated the OGLplus EGL-based example harness.