itree.[ch]: Add sanity checks, comments, and minor tweaks

* src/alloc.c (mark_overlay): Add sanity check.

* src/buffer.c (next_overlay_change, previous_overlay_change):
Tweak code to keep the same vars for the bounds.

* src/itree.c (interval_tree_clear, interval_tree_insert)
(interval_tree_remove, interval_tree_insert_fix, interval_tree_remove_fix):
Adjust to the `color` -> `red` change.
(interval_tree_clear): Prefer `true/false` for booleans.
(interval_generator_create): Use an actual `interval_tree_order` value
rather than 0.
(interval_generator_next): Simplify a tiny bit.  Add comment.
(interval_generator_narrow): Add sanity check.

* src/itree.h (struct interval_node): Replace `color` field with
boolean `red` field.
(enum interval_tree_order): Remove unused `ITREE_DEFLT_ORDER` value.

* src/pdumper.c (dump_interval_node): Adjust to the
`color` -> `red` change.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/pdumper.c b/src/pdumper.c
index 79644c01517..44486015f05 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -2154,7 +2154,7 @@ dump_interval_node (struct dump_context *ctx, struct interval_node *node,
   DUMP_FIELD_COPY (&out, node, offset);
   DUMP_FIELD_COPY (&out, node, otick);
   dump_field_lv (ctx, &out, node, &node->data, WEIGHT_STRONG);
-  DUMP_FIELD_COPY (&out, node, color);
+  DUMP_FIELD_COPY (&out, node, red);
   DUMP_FIELD_COPY (&out, node, visited);
   DUMP_FIELD_COPY (&out, node, rear_advance);
   DUMP_FIELD_COPY (&out, node, front_advance);