Fix clearing of the INCLUDE_DIRECTORIES DIRECTORY property.

This was broken by commit 18a3195a (Keep track of INCLUDE_DIRECTORIES
as a vector of structs., 2012-11-19).
try_compile: add missing fclose() to recently added error case

In commit 236133e7 (Handle targets in the LINK_LIBRARIES of try_compile,
2013-02-09) an error return case was added without closing the file in
progress.  Add the missing fclose() call.

Spotted by sevenhill.
get_filename_component: Document path components more clearly (#14091)

Organize component names in a table to explain each in more detail.
Clearly state that PATH is the directory name.
Merge topic 'fix-clear-INCLUDE_DIRECTORIES-prop'

5a5e0fa Fix clearing of the INCLUDE_DIRECTORIES DIRECTORY property.
Merge topic 'missing-fclose-in-trycompile'

ce441fa try_compile: add missing fclose() to recently added error case
Merge topic 'doc-get_filename_component'

df71f96 get_filename_component: Document path components more clearly (#14091)