ponk% cat chicken-include.scm 
#! /bin/sh
#| -*- scheme -*-
exec csi -s $0 -include-path /usr/local/share/scheme "$@"
|#

(include "something.scm")
ponk% strace ./chicken-include.scm 2>&1 | grep something
stat("something.scm.scm", 0x7fff16005c20) = -1 ENOENT (No such file or directory)
stat("something.scm.so", 0x7fff16005540) = -1 ENOENT (No such file or directory)
stat("something.scm", 0x7fff16005110)   = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm.scm", 0x7fff160042c0) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm.so", 0x7fff16003ba0) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm", 0x7fff16003760) = -1 ENOENT (No such file or directory)
open("something.scm", O_RDONLY)         = -1 ENOENT (No such file or directory)

ponk% cat chicken-include.scm                           
#! /bin/sh
#| -*- scheme -*-
exec csi -include-path /usr/local/share/scheme -s $0 "$@"
|#

(include "something.scm")
ponk% strace ./chicken-include.scm 2>&1 | grep something
stat("something.scm.scm", 0x7fffb1d78950) = -1 ENOENT (No such file or directory)
stat("something.scm.so", 0x7fffb1d78270) = -1 ENOENT (No such file or directory)
stat("something.scm", 0x7fffb1d77e40)   = -1 ENOENT (No such file or directory)
stat("/usr/local/share/scheme/something.scm.scm", 0x7fffb1d76ff0) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/scheme/something.scm.so", 0x7fffb1d768e0) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/scheme/something.scm", 0x7fffb1d764a0) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm.scm", 0x7fffb1d75720) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm.so", 0x7fffb1d75000) = -1 ENOENT (No such file or directory)
stat("/usr/local/share/chicken/something.scm", 0x7fffb1d74bc0) = -1 ENOENT (No such file or directory)
open("something.scm", O_RDONLY)         = -1 ENOENT (No such file or directory)