* Makefile.am (TESTS_ENVIRONMENT): Remove `guile' invocation. Add
semicolons, and export the variables as shown in the Automake 1.12
manual.
(LOG_COMPILER): New variable, with `guile' invocation.
* guix/derivations.scm: Export `read-derivation' and `write-derivation'.
* srfi/srfi-64.scm, srfi/srfi-64.upstream.scm: New files, from libchop.
* tests/derivations.scm, tests/test.drv: New files.