Fix bug in svn_config_has_section with handling case insensitive config.
- subversion/libsvn_subr/config.c (svn_config_has_section): Canonicalize the hash key.
- subversion/tests/libsvn_subr/config-test.c (test_has_section): Rename to test_has_section_case_insensitive(). (test_has_section_case_insensitive, test_has_section_case_sensitive): Expand to test different cases.
- subversion/tests/libsvn_subr/config-test.cfg (UpperCaseSection): Add new test section with capital letters.