It's clear that this change causes too many problems to be made
without warning. Revert the change disallowing conditional lines to
start with TAB.
Instead, generate warnings whenever a directive line begins with a
TAB character. Make this change for all directives, not just
conditional directives: define, undefine, export, unexport, vpath,
load, include, etc.
* NEWS: Update the backward-compatibility warning.
* src/read.c (eval): Track whether the line starts with a TAB.
If so then whenever we recognize a directive, emit a warning.
Revert the previous change for this bug.
(parse_var_assignment): Accept a file location if the line begins
with TAB; show a warning if we discover a directive.
(conditional_line): Warn about lines starting with TAB.
* tests/scripts/...: Add tests to verify warnings for initial TAB.
If a parent target has an exported variable that is private, don't
export it in child targets.
* NEWS: Mention this change.
* src/variable.c (target_environment): Ignore private inherited
variables.
* tests/thelp.pl: Add a new "env" operation to show env.var. values.
* tests/scripts/variables/private: Verify this new behavior.
