Remove cached schema entry when creating table

This fixes some corner cases, such as using raw SQL to drop a table
or dropping a table in another process.  However, it's safe as any
time create_table succeeds, any previous cached schema entry is
probably invalid.

lib/sequel/database/schema_methods.rb

@@ -89,6 +89,7 @@ def alter_table(name, generator=nil, &block)
     #
     # See Schema::Generator and the {"Migrations and Schema Modification" guide}[link:files/doc/migration_rdoc.html].
     def create_table(name, options={}, &block)
+      remove_cached_schema(name)
       options = {:generator=>options} if options.is_a?(Schema::Generator)
       generator = options[:generator] || Schema::Generator.new(self, &block)
       create_table_from_generator(name, generator, options)

spec/core/schema_spec.rb

@@ -23,6 +23,12 @@
     proc{@db.create_table(:cats.as(:c)) {}}.should raise_error(Sequel::Error)
   end
 
+  specify "should remove cached schema entry" do
+    @db.instance_variable_set(:@schemas, {'cats'=>[]})
+    @db.create_table(:cats){Integer :a}
+    @db.instance_variable_get(:@schemas).should be_empty
+  end
+
   specify "should accept multiple columns" do
     @db.create_table(:cats) do
       column :id, :integer