-I: Append to search list for include files

The fundamental search list for include files (read in via @i or @I) is defined by the environment variable FWEB_INCLUDES, which is a colon-delimited list such as

     setenv FWEB_INCLUDES .:/usr/fweb:/other/stuff
     

The -I option appends to this list.

For information about include files, see ATi.