From scripts/compile pushed default assumption of #:from as 'scheme down
into system/base/compile where filename and first line can be used to
deduce intended "from" language. If first line of a file is of the form
#lang ecmascript
then the file is assumed consist of source language "ecmascript".
* module/scripts/compile.scm (compile): changed default #:from to #f
from 'scheme
* module/system/base/compile.scm(lang-from-port, %file-extension-map,
add-lang-extension, lang-extension-for): added global
%file-extension-map with accessor lang-extension-for and updater
add-lang-extension. Also, added lang-from-port to parse first line,
looking for #lang.
* test-suite/tests.scm: added "load-lang" test.
* test-suite/Makefile.am(SCM_TESTS): added tests/load-lang.test
