function sFilePathAbs = liio_cksigfile(sFilePath, bWrite)
Checks <sFilePath> to determine the file to be written to if <bWrite> is true, or to be read from otherwise.
<sFilePath> might be an absolute or a relative path, or merely a bare file name. In the latter case it will be searched for on Matlab®'s path.
In case of reading, exactly one existing file must be determined that way, and this file must be readable with respect to current user privileges.
In case of writing, one or none existing file must be determined that way. In case of an exisitng file it will be checked for writability, othereise creatability of the file the path points to will be checked.
If all checks are successfull <sFilePathAbs> will contain the absolute path of the file determined for reading or writing, otherwise an error with a respective message will be thrown.
This function is mainly meant for the use from liio block-mask callbacks, but might be called for any other purpose as well.