PT-193 Fixed regex in TableParser

TableParser's parse function was failing while trying to lowercase
column names in the provided 'SHOW CREATE TABLE'.
The problem was it was trying to lowercase everything between backticks
but lines like these:

`field_name` int comment "here is a ` in the comment"
`second_field_name` int

made the original regex to fail, matching `in the coment"` as an
expression to be lowercased while second_file_name was considered as
outside backticks.

lib/TableParser.pm

@@ -145,7 +145,7 @@ sub parse {
 
    # Lowercase identifiers to avoid issues with case-sensitivity in Perl.
    # (Bug #1910276).
-   $ddl =~ s/(`[^`]+`)/\L$1/g;
+   $ddl =~ s/(`[^`\n]+`)/\L$1/gm;
 
    my $engine = $self->get_engine($ddl);
 

t/lib/TableParser.t

@@ -806,6 +806,32 @@ is_deeply(
    'issue with pairing backticks in column comments (issue 330)'
 );
 
+
+$tbl = $tp->parse( load_file('t/lib/samples/issue_pt-193_backtick_in_col_comments.sql') );
+is_deeply(
+   $tbl,
+   {  cols         => [qw(id f22abcde f23abc)],
+      col_posn     => { id => 0, f22abcde => 1, f23abc => 2 },
+      is_col       => { id => 1, f22abcde => 1, f23abc => 1 },
+      is_autoinc   => { id => 1, f22abcde => 0, f23abc => 0 },
+      null_cols    => [qw(f22abcde)],
+      is_nullable  => { f22abcde => 1},
+      clustered_key => undef,
+      keys         => {},
+      defs         => { id => "    `id` int(11) NOT NULL AUTO_INCREMENT", 
+                       "f22abcde" => "    `f22abcde` int(10) unsigned DEFAULT NULL COMMENT 'xxx`XXx'",   
+                       "f23abc" => "    `f23abc` int(10) unsigned NOT NULL DEFAULT '255' COMMENT \"`yyy\""
+                      },
+      numeric_cols => [qw(id f22abcde f23abc)],
+      is_numeric   => { id => 1, f22abcde => 1, f23abc => 1  },
+      engine       => 'InnoDB',
+      type_for     => { id => 'int', f22abcde => 'int', f23abc => 'int' },
+      name         => 't3',
+      charset      => 'latin1',
+   },
+   'issue with pairing backticks in column comments (issue 330)'
+);
+
 # #############################################################################
 # Issue 170: mk-parallel-dump dies when table-status Data_length is NULL
 # #############################################################################

t/lib/samples/issue_pt-193_backtick_in_col_comments.sql

@@ -0,0 +1,6 @@
+Create Table: CREATE TABLE `t3` (
+    `id` int(11) NOT NULL AUTO_INCREMENT,
+    `f22aBcDe` int(10) unsigned DEFAULT NULL COMMENT 'xxx`XXx',
+    `f23aBc` int(10) unsigned NOT NULL DEFAULT '255' COMMENT "`yyy",
+    PRIMARY KEY (`id`)
+) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1)