* Avoid continuously appending items to MANPATH and INFOPATH when
sourcing /etc/profile multiple times.
* Check for .bashrc existence in shell manager.
MSYSTEM now defaults to MSYS when not specified, and there is no
different behavior anymore between empty value and MSYS, for example
/opt/bin was not being added to path when not setting MSYSTEM. This
removes the need for explicitly setting the variable, since a default
value is now implied.
* New script /etc/msystem providing information associated with the
current MSYSTEM. This is sourced by /etc/profile but can be used by
non-login scripts for getting information such as the current
compiler architecture or mount point.
* New script /usr/bin/shell for switching between shells without
restarting MSYS2. This can be used in interactive sessions but also
from shell scripts for switching the MSYSTEM without restarting bash
or spawning a subshell.
* Allow /etc/profile to be sourced multiple times without continuously
appending stuff to PATH or losing track of the original Windows TEMP.
Also implemented for /etc/profile.d/perlbin.sh, so perl path is not
repeatedly appended.
The generic variable SET_FULL_PATH has been replaced with MSYS2_PATH_TYPE, which
can accept the following values:
* strict: no Windows path.
* inherit: full Windows path.
* Other values: minimal Windows path (default).
