Fix bug 578b7e273c03. -- Round computed end value to match precision … #4107

Job	Run time
msvc	10m 33s
msvc (CHECKS=nodep)	11m 3s
msvc (OPTS=static)	11m 8s
msvc (OPTS=noembed)	11m 4s
gcc	13m 18s
msvc (OPTS=symbols)	11m 0s
gcc (CFLAGS=-DTCL_NO_DEPRECATED=1)	13m 2s
msvc (OPTS=symbols STATS=compdbg,memdbg)	14m 19s
gcc (--disable-shared)	13m 23s
gcc (--disable-zipfs)	13m 1s
gcc (--enable-symbols)	13m 22s
gcc (--enable-symbols=mem)	14m 41s
gcc (--enable-symbols=all)	15m 10s
	2h 45m 4s

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