Fix invocations of guile function 'load-from-path'

The '.scm' extension prevents loading of a precompiled
version of the file from the %load-compiled-path and
will always trigger an autocompilation instead. Omitting
the extension properly allows the function to load a
precompiled version if it exists and is more recent than
the source file. This is only relevant for guile 2 but
works ok for guile 1.8 as well so it's changed unconditionally.
Rewrite old-fashioned makefile construct