cobol: Correct "included from" location.

When an error occurred in a copybook, the diagnostic reported the
location of the COPY directive incorrectly.  It now reports the
line of the directive.

The symbol table was recording paragraph/section relationships
incorrectly, which was only a problem if the last section PERFORMed.
Corrected.

Fixes PR #33 Fixes RT 3569.

gcc/cobol/ChangeLog:

	* cbldiag.h (struct cbl_loc_t): Add as_first_line() function.
	(location_dump): Shorten diagnostic message.
	* cdf-copy.cc (copybook_elem_t::open_file): Same.
	* copybook.h (class copybook_t): Remove debug message.
	* lexio.cc (parse_copy_directive): Clarify comment.
	(cdftext::lex_open): Set please_push_filename boolean for open_input.
	(cdftext::open_input): Issue push directive where COPY appeared.
	(cdftext::output_push_directive): New function.
	(cdftext::process_file): Relocate PUSH/POP directives.
	* lexio.h (class cdftext): Add please_push_filename and output_push_directive().
	* parse.y: Improve PERFORM diagnostics.
	* parse_ante.h (ast_enter_exit_section): Correct paragraph section ancestor.
	* scan.l: Update gcc location for PUSH directive.
	* symbols.cc (cbl_perform_tgt_t::recurses): New validation function.
	* symbols.h (struct cbl_perform_tgt_t): Same.
	* util.cc (cobol_filename): Clarify diagnostic message.
	(gcc_location_set_impl): Remove function.
	(gcc_location_set): Implement directly.
	(gcc_location_dump): Add newline to output.