glibc's iconv implementation supports ISO-6937-2, but libiconv doesn't
due to that these days the only place it's used is in a few old subtitle
formats. As a result, on everything but linux we need our own converter.
Conversion from ISO-6937-2 is currently not supported.
Originally committed to SVN as r6632.
Consistently use the C++ names for headers rather than a combination of the
C and C++ names.
Remove empty LAGI_PRE blocks.
Remove checks for both AGI_PRE and LAGI_PRE and change a check for only
AGI_PRE to LAGI_PRE.
Originally committed to SVN as r5516.
Thomas Goyne