There was no check for foreign keys when altering partitioned
tables.

Added check for FK when altering partitioned tables.

mysql-test/r/partition_innodb.result:
  Bug#50104: Partitioned table with just 1 partion works with fk
  
  Updated test result
mysql-test/t/partition_innodb.test:
  Bug#50104: Partitioned table with just 1 partion works with fk
  
  Added test for adding FK on partitioned tables (both 1 and 2
  partitions)
sql/sql_partition.cc:
  Bug#50104: Partitioned table with just 1 partion works with fk
  
  Disabled adding foreign key when altering a partitioned table.