A rule was introduced by the 5.1 part of the fix for bug 27531 to 
prefer filesort over indexed ORDER BY when accessing all of the rows of a 
table (because it's faster). This new rule was not accounting for the 
presence of a LIMIT clause.
Fixed the condition for this rule so it will prefer filesort over 
indexed ORDER BY only if no LIMIT.


mysql-test/r/compress.result:
  Bug #31094: LIMIT is not considered a full index scan
mysql-test/r/join.result:
  Bug #31094: test case
mysql-test/r/select.result:
  Bug #31094: LIMIT is not considered a full index scan
mysql-test/r/ssl.result:
  Bug #31094: LIMIT is not considered a full index scan
mysql-test/r/ssl_compress.result:
  Bug #31094: LIMIT is not considered a full index scan
mysql-test/t/join.test:
  Bug #31094: test case
sql/sql_select.cc:
  Bug #31094: prefer filesort over indexed ORDER BY only if no LIMIT