Fix wrong type

It reduces needless cast.
Place compared target at the left side
Fix a bug that the number of indexes isn't correct if index buffer is NULL
test: use new thread create function

g_thread_new() is used instead of
g_thread_create() because g_thread_create() is deprecated since
GLib 2.32.0.
Suppress deprecated warnings

    benchmark.c: In function 'bench_init':
    benchmark.c:26:5: warning: 'g_thread_init' is deprecated (declared at /usr/include/glib-2.0/glib/deprecated/gthread.h:260) [-Wdeprecated-declarations]
    benchmark.c:28:3: warning: 'g_type_init' is deprecated (declared at /usr/include/glib-2.0/gobject/gtype.h:669) [-Wdeprecated-declarations]
Extract a predicate that checks whether is the index valid
Support index section in match_columns

It supports:

    select Documents \
      --match_columns "Lexicon.index.section1 * 10 || Lexicon.index.section2" \
      --query "QUERY" \
      --output_columns "content, _score"
    # -> _score = (# of matches against section1) * 10 + (# of matches against section2)
Support outside build directory again
Really support outside build directory again (maybe...)
Really really support outside build directory (maybe...)
Use builddir for generated files
Create empty ChangeLog for "make dist"
test: group index section tests
Clear weight vector after search
Support index section by index in match_columns

It supports:

    select Documents \
      --match_columns "Lexicon.index[0] * 10 || Lexicon.index[1]" \
      --query "QUERY" \
      --output_columns "content, _score"
    # -> _score = (# of matches against section 1) * 10 + (# of matches against section 2)
Define COND_BROADCAST (Thanks to t2001).
Fix a typo
Add tokenize command

TODO: document
Show system error message on mmap() is failed

It is tested by changing grn_io_seg_map_() like:

     void
     grn_io_seg_map_(grn_ctx *ctx, grn_io *io, uint32_t segno, grn_io_mapinfo *info)
     {
    +   errno = ENOMEM;
    +   return;
        SEG_MAP(io, segno, info);
     }

NOTE: Windows version may not be worked. I didn't try it yet.
Make Windows version grn_current_error_message() buildable