Variables extension: added proper trace support.

src/lib-sieve/plugins/include/cmd-global.c

src/lib-sieve/plugins/include/ext-include-binary.c

src/lib-sieve/plugins/include/ext-include-binary.h

src/lib-sieve/plugins/include/ext-include-common.c

src/lib-sieve/plugins/include/ext-include-variables.c

src/lib-sieve/plugins/include/ext-include-variables.h

src/lib-sieve/plugins/variables/cmd-set.c

src/lib-sieve/plugins/variables/ext-variables-common.c

src/lib-sieve/plugins/variables/ext-variables-common.h

src/lib-sieve/plugins/variables/ext-variables-dump.c

src/lib-sieve/plugins/variables/ext-variables-operands.c

src/lib-sieve/plugins/variables/sieve-ext-variables.h

src/lib-sieve/sieve-runtime-trace.h