Code cleanup: parser, lexer, lda-plugin and main interface.

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.c

src/lib-sieve/sieve.h

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