[pdftex] Correction to pdftex-a.pdf

[Karl Berry]

Hi Gernot,

    Date: Thu, 1 Dec 2016 14:01:30 +0900
    ...
    "If the fontflags field is not given, pdfTEX treats it as being 4, a
    symbolic font."
    Problem: 4 is script font, symbolic font is 3 according to Table 3.

Coming back to this: actually, both the documentation and the code are
correct, if not a model of clarity. Table 3 shows bit positions, not
decimal values. The decimal value "4" means that bit position 3 is set
-> symbolic font.

What was omitted from the manual is that this is the default for
embedded fonts. For non-embedded fonts (not that anyone should be using
those), the default is 0x22.

I added a few more words of description.  --thanks, karl.