Internally just store the conditionals as space separated lists of

Internally just store the conditionals as space separated lists of
CONDITIONS (instead of @CONDITIONS@).
* automake.in (&conditional_true_when, &variable_conditions_sub):
Split conditions at spaces.
(&handle_dependencies, &variable_conditions_permutations): Don't
put @ around conditions.
(&variable_conditions_cmp): There are no @ to strip.
(&make_condition): New.
(&define_pretty_variable, &read_main_am_file, &read_am_file): Use
it.
(&read_main_am_file, &read_am_file): Stop playing with @ by hand.
Join @conditional_stack with spaces.
(&read_main_am_file): Adjust the output of variables.
Output `TRUE = true' under the condition `TEST' as `@TEST@TRUE =
true' and no longer `@TEST@TRUE = @TEST@true'.
(&variable_conditions_cmp): Rename as...
(&by_condition): this.
Sort in a human pleasant order.
Use it everywhere a human can see conditions.
(&variable_conditions_reduce): Don't sort conditions, that's
pointless.
* tests/cond.test, ctarget1.test, pluseq3.test: Strengthen.