[ft] How to get nominal width of monospaced fonts

[Sam Varshavchik]

I'm trying to determine the nominal width of monospaced fonts, in pixels,  
that is the normal horizontal advance of rendered glyphs when  
FT_FACE_FLAG_FIXED_WIDTH is set.

I thought, at first, to look at face->size->metrics.max_advance, but if I do  
that I find that it's always several pixels more than what I eventually get  
after FT_LOAD_RENDERing each glyph, and computing face->glyph->advance.x >> 6.

For example, using Liberation Mono: with a height of 16 pixels, I get 11 
in metrics.max_advance, but the actual advance width, based on advance.x, is  
10. With a height of 21 pixels, I get a max_advance of 15, and the actual  
advance based on advance.x is 13. Is it possible to get the advance width,  
of fixed width fonts, without actually rendering some sample glyphs and  
seeing what it is?