pack.pl: Update file perms for db header files

[shawnlaffan]

The db header files are coming out as readonly. We could fix this in the build but it might be easier to run the update when packing.

A variation of this line to handle header files should do the trick.

build-extlibs/pack.pl

Line 1130 in 56e3a3b

$f->unixFileAttributes(0777) if $dst =~ /\.(exe|bat|dll)$/i; # necessary for correct unzipping on cygwin