use Basic Regular Expressions - BRE for sed and grep - related to #44

use BRE increase portability, special for sed
 where there a different option to turn on Extended Regular Expressions
 for the GNU sed (-r) and the BSD sed (-E).
 POSIX does not mean always portability,
 so that try reduce whitespace characters to spaces [ ] instead of [[:spaces:]] or [[:blank:]] (NB. tested on smartOS)
don't overwrite empty file during VBOX_VERSION autoupdate
make sure that history expansion is turned off