For PR automake/360:

For PR automake/360:
* lib/Automake/Location.pm: New file.
* lib/Automake/Channels.pm (_print_message): Display contexts
when given an Automake::Location.
(msg): Clone the location.
* lib/Automake/Makefile.am (dist_perllib_DATA): Add Location.pm.
* tests/comment5.test: Make sure we display `included from' stacks.
* automake.in: Use Automake::Location.
(INTERNAL): New constant.
(file_contents, file_contents_internal, define_variable,
define_pretty_variable, read_am_file): Take $WHERE as argument.
Adjust all callers.
(scan_autoconf_traces) <$where>: Define as a Location, and use
it instead of $here.
(macro_define, rule_define): Make sure $WHERE is a location.
Clone it before updating $var_location or $targets.