Log Message:
Update to 6.4:

Version 6.4 - March 24 2015

[CHANGES]
New facilities:
o gtags: Now --sqlite3 option is supported formally. This option uses
  SQLite3 API instead of BSD/DB API for making tag files.
  To use this option, you need to invoke configure script with
  --with-sqlite3 in the build phase.

        [configuration phase]
        $ ./configure --with-sqlite3    # use sqlite3 API

        [execution phase]
        $ gtags --sqlite3               # make sqlite3 tag files

o gtags: --single-update option supports deletion of a file.
  Now the next command line works well.

	$ rm test.c
	$ gtags --single-update=test.c

o gtags: New --explain option. This option explains handling files.
  You can know the following information:
  - Skipped reason for each skipped files.
  - Used parser and its library path for each source file.

[FIXED BUGS]
o global: global(1) could not pick up source code from source files
  in library projects (GTAGSLLIBPATH) if their tag files are compact
  format. Now it works.

[INCOMPATIBLE CHANGES]
The following features of htags(1) were removed.
o The -c (--compact) option.
o The --system-cgi option.
o The --overwrite-key option.
o The -x (--xhtml[=version]) option.
  All files are 1.0.
o The following configuration variables:
  colorize-warned-line (substitute: --colorize-warned-line)
  gzipped_suffix (substitute: not available)
  htags_options (substitute: HTAGS_OPTIONS)
  ncol (substitute: -n, --line-number [n])
  normal_suffix (will be always '.html')
  no_order_list (substitute: --no-order-list)
  script_alias (substitute: not available)
  tabs (substitute: --tabs n)
  xhtml_version (will be always 1.0)