allow any number of -e and -f options

Allow any number of -e and -f options.  They are concatenated as if
they were given as one big string.  This allows for a bit nicer
scripting use in some situations, e.g., passing a parameter:

    dwgrep -e "let X := \"$1\";" -e 'rest of script'
make "-" mean stdin

This changes the -f option so that "-f -" means to read from stdin.
The patch itself is quite ugly as I didn't see a much nicer way of
doing this.
update .gitignore

This updates .gitignore for in-tree builds.
don't include libzwerg-dw.h