Bug#55873 short startup options do not work in 5.5

Before this fix, the server did not recognize 'short' (as in -a)
options but only 'long' (as in --ansi) options
in the startup command line, due to earlier changes in 5.5
introduced for the performance schema.

The root cause is that handle_options() did not honor the
my_getopt_skip_unknown flag when parsing 'short' options.

The fix changes handle_options(), so that my_getopt_skip_unknown is
honored in all cases.

Note that there are limitations to this,
see the added doxygen documentation in handle_options().

The current usage of handle_options() by the server to
parse early performance schema options fits within the limitations.
This has been enforced by an assert for PARSE_EARLY options, for safety.

mysql-test/suite/perfschema/r/bad_option_3.result

@@ -0,0 +1,2 @@
+Found: unknown option '-x'
+Found: Aborting

mysql-test/suite/perfschema/r/bad_option_4.result

@@ -0,0 +1,2 @@
+Found: Can't change dir to.*bad_option_h_param
+Found: Aborting

mysql-test/suite/perfschema/r/bad_option_5.result

@@ -0,0 +1,2 @@
+Found: unknown option '-X'
+Found: Aborting

mysql-test/suite/perfschema/r/short_option_1.result

@@ -0,0 +1,27 @@
+select 'Ok, the server started' as result;
+result
+Ok, the server started
+select @@SQL_MODE;
+@@SQL_MODE
+REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ANSI
+show variables like 'sql_mode';
+Variable_name	Value
+sql_mode	REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ANSI
+select @@character_set_server;
+@@character_set_server
+utf8
+show variables like 'character_set_system';
+Variable_name	Value
+character_set_system	utf8
+show variables like 'log';
+Variable_name	Value
+log	ON
+show variables like 'general_log';
+Variable_name	Value
+general_log	ON
+show variables like 'new';
+Variable_name	Value
+new	ON
+show variables like 'log_warnings';
+Variable_name	Value
+log_warnings	3

mysql-test/suite/perfschema/r/short_option_2.result

@@ -0,0 +1,9 @@
+select 'Ok, the server started' as result;
+result
+Ok, the server started
+select @@SQL_MODE;
+@@SQL_MODE
+REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ANSI
+select @@log_warnings;
+@@log_warnings
+5