system: Add locale to boot-parameters.

* gnu/system.scm (<boot-parameters>): New locale field.
(boot-parameters-locale): New accessor.
(read-boot-parameters): Read locale field.
(operating-system-boot-parameters): Add locale to boot-parameters form.
(opeating-system-boot-parameters-file): Add locale to file-like object.
* tests/boot-parameters.scm: New test file.
* Makefile.am (SCM_TESTS): Add tests/boot-parameters.scm.
---
 Makefile.am               |   1 +
 gnu/system.scm            |  19 +++-
 tests/boot-parameters.scm | 232 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 248 insertions(+), 4 deletions(-)