digest works in the proxyauth too

docs/libcurl/curl_easy_setopt.3

@@ -442,7 +442,7 @@ use. Note that for some methods, this will induce an extra network
 round-trip. Set the actual name and password with the
 \fICURLOPT_PROXYUSERPWD\fP option. The bitmask can be constructed by or'ing
 together the bits listed above for the \fICURLOPT_HTTPAUTH\fP option. As of
-this writing, only Basic and NTLM work. (Added in 7.10.7)
+this writing, only Basic, Digest and NTLM work. (Added in 7.10.7)
 .SH HTTP OPTIONS
 .IP CURLOPT_AUTOREFERER
 Pass a non-zero parameter to enable this. When enabled, libcurl will