Fixed build configuration for LCOV and Gcovr.

* jamroot: Changed include paths to absolute ones because Gcovr seems to
           require absolute filenames in order to produce correct branch
           coverage reports.
* src/container/jamfile: Changed to use `modules.binding` rule to extract
                         the path to itself, as described in Boost.Build
                         document.
* src/exception/jamfile: Likewise.
* src/functional/jamfile: Likewise.
* src/memory/jamfile: Likewise.
* src/mpl/jamfile: Likewise.
* src/scope_guard/jamfile: Likewise.
* src/type_traits/jamfile: Likewise.
* src/unicode/jamfile: Likewise.
* src/utility/jamfile: Likewise.
* test/jamfile: Deleted unused lines.
* test/unit/container/jamfile: Changed to use `modules.binding` rule to
                               extract the path to itself, as described in
                               Boost.Build document.
* test/unit/exception/jamfile: Likewise.
* test/unit/functional/jamfile: Likewise.
* test/unit/jamfile: Likewise.
* test/unit/memory/jamfile: Likewise.
* test/unit/memory/polymorphic_allocator/jamfile: Likewise.
* test/unit/mpl/jamfile: Likewise.
* test/unit/scope_guard/jamfile: Likewise.
* test/unit/type_traits/jamfile: Likewise.
* test/unit/unicode/jamfile: Likewise.
* test/unit/utility/jamfile: Likewise.
* test/coverage/jamfile: Likewise.
* test/coverage/lcov/jamfile:
  * Changed to use `modules.binding` rule to extract the path to itself, as
    described in Boost.Build document.
  * Added `--config-file` option to `lcov` and `genhtml` commands in order
    to produce branch coverage.
* test/coverage/lcov/lcovrc: Newly added. The file specified in
                             `--config-file` option.
* test/coverage/gcovr/jamfile:
  * `Changed to use `modules.binding` rule to extract the path to itself, as
    described in Boost.Build document.
  * Added `--exclude-unreachable-branches` option to `gcovr` command.
Fixed bugs.

* test/coverage/lcov/jamfile: Handle possible cases where the current
                              working directory (the locaiton where `bjam`
                              is invoked) is different from
                              `$(CRADLE_ROOT)`.
* test/coverage/gcovr/jamfile: Likewise.
Merge pull request #28 from Cryolite/fix/coverage

Fixed test coverage reports.