bug#20793: 25.0.50; Some Unicode glyphs aren't monospaced

[Oleh Krehel <ohwoeowho@gmail.com>]

My preferred font is "DejaVu Sans Mono".  When using the Unicode
character "✜", its width is more than the standard char width. This
causes alignment problems for me.

This issue doesn't occur in Emacs 24.5.2. There, the char has the same
width as all others.

Details on the char in Emacs 25:

             position: 227 of 348 (65%), column: 35
            character: ✜ (displayed as ✜) (codepoint 10012, #o23434, #x271c)
    preferred charset: unicode (Unicode (ISO10646))
code point in charset: 0x271C
               script: symbol
               syntax: w 	which means: word
             category: .:Base
             to input: type "C-x 8 RET 271c" or "C-x 8 RET HEAVY OPEN CENTRE CROSS"
          buffer code: #xE2 #x9C #x9C
            file code: #xE2 #x9C #x9C (encoded by coding system utf-8-emacs-unix)
              display: by this font (glyph code)
    xft:-unknown-Symbola-normal-normal-semicondensed-*-15-*-*-*-*-0-iso10646-1 (#x9F9)

Character code properties: customize what to show
  name: HEAVY OPEN CENTRE CROSS
  old-name: HEAVY OPEN CENTER CROSS
  general-category: So (Symbol, Other)
  decomposition: (10012) ('✜')

There are text properties here:
  fontified            t

Details on the char in Emacs 24.5.2:

             position: 1819 of 2174 (84%), column: 5
            character: ✜ (displayed as ✜) (codepoint 10012, #o23434, #x271c)
    preferred charset: unicode (Unicode (ISO10646))
code point in charset: 0x271C
               script: symbol
               syntax: w 	which means: word
             category: .:Base
             to input: type "C-x 8 RET HEX-CODEPOINT" or "C-x 8 RET NAME"
          buffer code: #xE2 #x9C #x9C
            file code: #xE2 #x9C #x9C (encoded by coding system utf-8-unix)
              display: by this font (glyph code)
    xft:-unknown-DejaVu Sans Mono-normal-normal-normal-*-15-*-*-*-m-0-iso10646-1 (#xAD1)