make full_export: Subtract on different types.

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1017

Reported by Fredrik Noring, Roxen Internet Software noring@roxen.com

make full_export gives:

Creating tag v7_1_34 in the background.
vpath = Pike-v7.1.34  pwd = /home/distmaker/Distmaker/2.2/build
Subtract on different types.
Unknown program: `-(0,({"CVS","RCS",".cvsignore"}))
pike-cvs/bin/export.pike:26: get_files("Pike-v7.1.34/src")
pike-cvs/bin/export.pike:201:
main(2,({"/home/distmaker/Distmaker/2.2/build/pike-cvs/bin/export.pike"}))
make[2]: *** [full_export] Error 10
make[2]: Leaving directory
`/home/distmaker/Distmaker/2.2/build/pike.srcbuild'