bug#30308: [PATCH v2] Support standard Terminfo direct mode terminals.

[Eli Zaretskii]

> From: Rami Ylimäki <rami.ylimaki@vincit.fi>
> Date: Thu,  1 Feb 2018 11:41:33 +0200
> 
> Latest Terminfo introduces terminal definitions that support direct
> color mode.  The "Co"/"colors" capability is set to 0x1000000 on these
> terminals and Emacs is already compatible with them.
> 
> However, if used Terminfo library hasn't been compiled with 32-bit
> value support, "Co"/"colors" is truncated to 0x7fff.  In this case
> direct color mode support can be detected from the "RGB" capability
> flag.
> 
> There are some minor problems if the color count isn't corrected from
> 0x7fff.  First eight standard colors defined in xterm-standard-colors
> are shown correctly.  However, their RGB values match the terminal
> settings, not the RGB values defined in xterm-standard-colors.  Bright
> versions of these colors are shown incorrectly.  They are interpreted
> as pixels #000008 - #000015, which are very dark shades of blue.
> 
> * src/term.c (init_tty): Force terminal color count to 0x1000000 if
>   "RGB" capability is present.
> * src/tparam.h: Define prototype for tigetflag.
> 
> * doc/misc/efaq.texi (Colors on a TTY): Add information about direct
>   mode terminals supported by Terminfo.

Thanks, pushed to the master branch.