Bug #18199 PURGE BINARY LOGS fails silently with missing logs;

Bug #18453  Warning/error message if there is a mismatch between ...
 
There were three problems:
 
 1. the reported lack of warnings for the BEFORE syntax of PURGE;
 2. the similar lack of warnings for the TO syntax;
 3. incompatible behaviour between the two in that the latter blanked out
    regardlessly of presence or lack the actual file corresponding to
    an index record; the former version gave up at the first mismatch.

fixed with deploying the warning's generation and synronizing logics of 
purge_logs() and purge_logs_before_date().
my_stat() is called in either of two branches of purge_logs() (responsible
for the TO syntax of PURGE) similarly to how it has behaved in the BEFORE syntax.
If there is no actual binlog file, my_stat returns NULL and my_delete is
not invoked.
A critical error is reported to the user if a file from the index
could not be retrieved info about or deleted with a system error code
different than ENOENT.

mysql-test/include/show_binary_logs.inc

@@ -0,0 +1,3 @@
+--replace_result $MYSQLTEST_VARDIR MYSQLTEST_VARDIR
+--replace_column 2 #
+show binary logs;