Allow multiple image activators to run on the same execution by changing
imgp->interpreted to a bitmask instead of, functionally, a bool. Each
imgactivator now requires its own flag in interpreted to indicate whether
or not it has already examined argv[0].

Change imgp->interpreted to an unsigned char to add one extra bit for
future use.

With this change, one can execute a shell script from a 64bit host native
make and still get the binmisc image activator to fire for the script
interpreter. Prior to this, execution would fail.

Phabric: https://reviews.freebsd.org/D696
Reviewed by: jhb@
MFC after: 4 weeks