doc: typo: s/can not/cannot/ and s/is does/does/

"Can not" suggests one has the option to not do something, whereas
"cannot" more strongly suggests something is disallowed or impossible.

Noticed "can not", mistakenly used instead of "cannot" in git help
glossary, then ran git grep 'can not' and found many other instances.
Only files in the Documentation folder were modified.

'Can not' also occurs in some source code comments and some test
assertion messages, and there is an error message and translation "can
not move directory into itself" which I may fix and submit separately
from the documentation change.

Also noticed and fixed "is does" in git help fetch, but there are no
other occurrences of that typo according to git grep.

Signed-off-by: Mark Rushakoff <mark.rushakoff@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-cvsserver.txt b/Documentation/git-cvsserver.txt
index f98b7c6..79e22b1 100644
--- a/Documentation/git-cvsserver.txt
+++ b/Documentation/git-cvsserver.txt
@@ -232,7 +232,7 @@
 'git-cvsserver' write access to the database file without granting
 them write access to the directory, too.
 
-The database can not be reliably regenerated in a
+The database cannot be reliably regenerated in a
 consistent form after the branch it is tracking has changed.
 Example: For merged branches, 'git-cvsserver' only tracks
 one branch of development, and after a 'git merge' an