If someone provides a --prefix that ends with slash, strip the slash.
tree1c3fdb6d87802b71bb23d7a4786aee8252e0faea
-rw-r--r-- 33 .gitignore
-rw-r--r-- 313 Makefile
-rw-r--r-- 211 README
-rw-r--r-- 2225 asciidoc.conf
lrwxrwxrwx 14 git-subtree -> git-subtree.sh
-rwxr-xr-x 11999 git-subtree.sh
-rw-r--r-- 10315 git-subtree.txt
-rw-r--r-- 1192 manpage-base.xsl
-rw-r--r-- 475 manpage-normal.xsl
-rw-r--r-- 23 shellopts.sh
-rwxr-xr-x 4381 test.sh
-rw-r--r-- 1733 todo