Add error codes to apr_errno.h

[jean-frederic clere]

Hi,

I am planning to add two new error codes to apr_errno.h for apr-iconv:
APR_EILSEQ Illegal byte sequence
APR_E2BIG  Too big (It can be used also for "Arg list too long").

Any comments? - I have already added APR_EFTYPE -

Cheers

Jean-frederic