Corrected Use of CMake Variable

[ghost]

The project uses CMAKE_SOURCE_DIR to refer to the top level directory of the project, when it should be using PROJECT_SOURCE_DIR.

• CMAKE_SOURCE_DIR refers to the directory from which CMake was started.
• PROJECT_SOURCE_DIR refers to the directory from which project(qaccordion) was called.

It's not always the case that CMAKE_SOURCE_DIR is the same as PROJECT_SOURCE_DIR. If qaccordion is included into another project, the variables are different.

For instance, if qaccordion is in another project like other-project/external/qaccordion, then:

• CMAKE_SOURCE_DIR is /home/tay10r/other-project/
• PROJECT_SOURCE_DIR is /home/tay10r/other-project/external/qaccordion