lib-sieve: variables extension: Made the maximum scope and variable size configurable.

INSTALL

doc/extensions/variables.txt

src/lib-sieve/plugins/imap4flags/ext-imap4flags-common.c

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

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

src/lib-sieve/plugins/mime/cmd-extracttext.c

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

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

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

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

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

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

src/plugins/sieve-extprograms/cmd-execute.c