S9fES  (locate-file string)  ==>  string | #f

Attempt to locate the file specified in STRING in a pre-defined set
of directories. The directories to search are stored as strings in
the *LIBRARY-PATH* variable. LOCATE-FILE appends a slash (/) and the
given file name to each path of *LIBRARY-PATH* and then checks the
existence of the resulting fully qualified file name by using
FILE-EXISTS?. It returns the first fully qualified file name that
exists or #F in case the file could not be located.

; Given *LIBRARY-PATH* = ("." "/u/s9fes")
; and hello.scm in /u/s9fes/examples

(locate-file "examples/hello.scm")  ==>  "/u/s9fes/examples/hello.scm"
(locate-file "non-existent")        ==>  #f

Rationale: LOCATE-FILE is intended to locate files that belong to
the S9fES system, like system library files, user library files,
and help files. The value of *LIBRARY-PATH* is initialized when the
Scheme 9 system starts up, for example by copying it from the
S9FES_LIBRARY_PATH environment variable.
