Warn about unknown format strings in the Mercury system.

*/*_FLAGS.in:
    Specify that by default, the compiler should generate warnings
    for unknown format strings and bad known format strings.

*/Mercury.options:
    Override this default setting for a few modules that have legitimate
    reasons for calling e.g. string.format with unknown format strings.

compiler/fact_table.m:
deep_profiler/html_format.m:
    Minor changes to avoid calling string.format with unknown format strings.

mfilterjavac/MFILTERJAVAC_FLAGS.in

@@ -1,5 +1,7 @@
 @BOOTSTRAP_MC_ARGS@
 --no-infer-all
+--warn-known-bad-format-calls
+--warn-unknown-format-calls
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir