Fix long standing logic bug in basename() introduced in 1.4.

Fix long standing logic bug in basename() introduced in 1.4.

We do not want to copy MAXPATHLEN/sizeof(bname) with strlcpy() since that will
happily copy ANY trailing slash, negating the entire pointer arithmatic of
endp and startp above.
Instead, reinstate endp - startp as size parameter to the copy function.
However, normally where a + 1 would be needed to solve the outcome, we now need
+ 2 due to strlcpy() only copying *size - 1*.