Make g_enum_get_value_by_name(), g_flags_get_value_by_name(),
g_enum_get_value_by_nick() and g_flags_get_value_by_nick() perform ASCII
case-insensitive comparisons when matching names and nicks. This aligns
behavior with common expectations for user-visible nicks and reduces
rejections of mixed-case inputs.
Implementation switches from strcmp() to strcmp_ignore_case() when
comparing the provided name/nick to registered values.
This is a minor behavior change that only broadens accepted input. Types
with values that differ only by case are now allowed.
Tests: Extend gobject/tests/enums.c to cover mixed-case lookups for both
enums and flags (names and nicks).
Fixes: #74
c4718596c2