Shows text roughly correctly, but many problems. Conditional at
run-time on the SAL_ENABLE_GLYPH_CACHING environment variable in
addition to SAL_FORCEGL.

One obvious thing that needs fixing is making sure that the glyphs are
rendered into the texture without overlap. Compensating negative
values in the ABC::abcA and ABC::abdC width is not enough.

Also, the cache should be changed to actually have "cache"
functionality, i.e. entries should expire based on some criterion.

Change-Id: I66a37d3354a09011a654f15a7d2bd8efaa14ad1e