Cannot compile nnimap

["Jari Mäkelä" <jmakela@terranova.fi>]

There are two errors I get when compiling the nnimap-0.3.31. One about
missing functions and another about doc string file or whatever:

emacs -batch -q -no-site-file -f batch-byte-compile hmac.el
Wrote /home/jmakela/nnimap-0.3.31/hmac.elc
Done
emacs -batch -q -no-site-file -l hmac.elc -f batch-byte-compile imap.el
While compiling the end of the data in file
/home/jmakela/nnimap-0.3.31/imap.el:
  ** The following functions are not known to be defined:  remassoc,
    base64-decode-string, base64-encode-string, int-char, char-int,
    object-plist, destructive-plist-to-alist
Wrote /home/jmakela/nnimap-0.3.31/imap.elc
Done
emacs -batch -q -no-site-file -l imap.el -f batch-byte-compile nnimap.el
Cannot open doc string file "/usr/share/emacs/20.2/etc/DOC-20.2.1"
make: *** [nnimap.elc] Error 255

Is my Emacs or nnimap broken? Am I missing some package? Any help?

Version information:
GNU Emacs 20.2.1
Gnus v5.6.44
nnimap 0.3.31

Jari