Update to 0.7:

* Added build-time checks to atf-c and atf-c++. A binding for atf-sh
  will come later.

* Migrated all build-time checks for header files to proper ATF tests.
  This demonstrates the use of the new feature described above.

* Added an internal API for child process management.

* Converted all plain-text distribution documents to a Docbook canonical
  version, and include pre-generated plain text and HTML copies in the
  distribution file.

* Simplified the contents of the Makefile.am by regenerating it from a
  canonical Makefile.am.m4 source. As a side-effect, some dependency
  specifications were fixed.

* Migrated all checks from the check target to installcheck, as these
  require ATF to be installed.

* Fixed sign comparison mismatches triggered by the now-enabled
  -Wsign-compare.

* Fixed many memory and object leaks.

(jmmv)