[core] add ReactOS support

* Use Syslinux v4 and mboot.c32 to chainload setupldr.sys
* Closes #266
[misc] minor improvements to the About dialog

* Bigger dialog, larger font, etc.
* Also fix a MinGW warning in parser.c
[loc] use the system message font for notifications

* Vista and later use a different system message font than MS Shell Dlg
* For languages such as Chinese, it makes custom notifications look quite
  different from system ones, which is not what we want
* Issue reported by Wayne Ying