Further developed error handling.

src/lib-sieve/sieve-ast.c

src/lib-sieve/sieve-ast.h

src/lib-sieve/sieve-error.c

src/lib-sieve/sieve-error.h

src/lib-sieve/sieve-lexer.c

src/lib-sieve/sieve-lexer.h

src/lib-sieve/sieve-parser.c

src/lib-sieve/sieve-parser.h

src/lib-sieve/sieve-validator.c

src/lib-sieve/sieve.c

src/lib-sieve/sieve.h

src/plugins/lda-sieve/lda-sieve-plugin.c

src/sieve-bin/bin-common.c

src/sieve-bin/sievec.c