Don't use "boolean" as variable name #370

Job	Run time
build (gcc)	1m 38s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 38s
build (gcc, --disable-xft)	1m 57s
test (gcc)	4m 3s
test (gcc, --disable-xft)	4m 30s
build (gcc, --disable-xss)	2m 5s
test (gcc, --enable-symbols)	3m 21s
build (gcc, --enable-symbols)	1m 25s
build (clang)	1m 48s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 9s
build (clang, --disable-xft)	1m 47s
build (clang, --disable-xss)	2m 11s
build (clang, --enable-symbols)	1m 25s
	29m 57s

Provide feedback