select: rename --query_expansion to --query_expander for consistency

Other parameter names such as --scorer and --default_tokenizer uses
"-er" style but --query_expansion doesn't use it. So --query_expansion
is renamed to --query_expander.

--query_expansion is deprecated but it can be used. If both of
--query_expansion and --query_expander are used, --query_expander is
--used and --query_expansion is ignored.

Test files are renamed to adapt this speicication change:

  test/command/suite/select/query_expansion/query_expander/ ->
  test/command/suite/select/query_expander/proc/

  test/command/suite/select/query_expansion/* ->
  test/command/suite/select/query_expander/column/

test/command/suite/select/query_expander/* are added for backward
compatibility check.
doc: update for renaming --query_expansion to --query_expander

TODO: .po should be updated in release process for this month. :p