algorithm (needed for the file selector and useful for other purposes, like
assembling lists of livery or screenshot files etc.)
- io.nas: move fixpath to string.nas (it's not only useful for file paths
but can also be used for property paths)
- screen.nas: move trim to string.nas (used by screen.nas and nasal-console.xml)
- gui.nas: add pattern matching to FileSelctor
- ufo.nas: use patterm matching (only *.ac and *.xml files shall be listed)
a side effect of the stack loop already
- replace all backslashes by slashes, to avoid security problems on UNIX
(if support for them is desirable on MS Windows, then we'd need an OS
property)
