MSYSTEM is now explicitly set to MSYS, so /opt/bin is added to system
path and related build failures are avoided, for example for packages
using mingw-w64-cross-gcc.
* Update pacman to latest version for performing the AppVeyor core
update instead of explicitly referencing the core packages. Missing
references would cause the just upgraded pacman to detect a still
required core update in ci-build script, where it is supposed to
perform a regular update instead.
* Enable downgrades in ci-build script and AppVeyor so package versions
removed from pacman repositories are properly reverted.
* Install git as required by ci-build script.
* Only build packages that are actually present in source tree.
This should fix detection of renamed package folders, including case
sensitivity changes.
* Fix case sensitivity of Bintray account names.
Bintray accounts are now properly referenced in lowercase, and compared
without case sensitivity against the GitHub account for enabling deployment.
* Initialize target list when converting lines to array.
A pacman repository is now generated with built packages, and exported by
AppVeyor to Bintray. Similar export can now be implemented for Drone, and
services other than Bintray can also be used.
