reinit grn_obj in rb_grn_bulk_from_ruby_object_with_type()

type of bulk may be changed in other conversion functions
Test for assigning column value by Int32 after String
Merge pull request #27 from rutice/fix-assign-column2

Fix assigning column value by Integer after String

Patch by rutice. Thanks!!!
test: fix indent
test: group operation tests
test: indent
test: add "n_" prefix for "the number of" value column
test: check assigned value instead of checking not raised
test: fix expected value
Fix indent
Fix a memory leak in Groonga::PatriciaTrie.open_near_cursor
Simplify
Use domain on initialization to reduce reinit
doc: fix a typo

Rrroonga ->
Rr oonga
  -
doc: use "Rroonga" form
doc tutorial: remove needless option

"-rubygems" option is enabled by default since Ruby 1.9.
doc tutorial: add space between option and value
doc install: remove needless extention

".bat" is usually omitted.
doc install: use ">" as prompt in Windows
Fix Column#rename to set new name on grn_named_object