html-tidy: unify with its drop-in replacement tidy-html5

- the original project has been unmaintained for years
- some dependants needed to be patched due to renamed headers
  https://github.com/htacg/tidy-html5/issues/326#issuecomment-160329114
- separate tidy-html5 package was removed, as since the 5.0.0 version
  it's meant as a successor to both, and library name got back
  from libtidy5.so to libtidy.so
  https://github.com/htacg/tidy-html5/issues/326#issuecomment-160314666

/cc committers to tidy-html5: @edwjto and @zimbatm.

pkgs/servers/prayer/default.nix

@@ -6,17 +6,12 @@ let
 in
 stdenv.mkDerivation rec {
   name = "prayer-1.3.5";
-  
+
   src = fetchurl {
     url = "ftp://ftp.csx.cam.ac.uk/pub/software/email/prayer/${name}.tar.gz";
     sha256 = "135fjbxjn385b6cjys6qhbwfw61mdcl2akkll4jfpdzfvhbxlyda";
   };
 
-  buildInputs = [ openssl db zlib uwimap html-tidy pam ];
-  nativeBuildInputs = [ perl ];
-
-  NIX_LDFLAGS = "-lpam";
-
   patches = [ ./install.patch ];
   postPatch = ''
     sed -i -e s/gmake/make/ -e 's/LDAP_ENABLE.*= true/LDAP_ENABLE=false/' \
@@ -26,8 +21,16 @@ stdenv.mkDerivation rec {
       Config
     sed -i -e s,/usr/bin/perl,${perl}/bin/perl, \
       templates/src/*.pl
+  '' + /* html-tidy updates */ ''
+    substituteInPlace ./session/html_secure_tidy.c \
+      --replace buffio.h tidybuffio.h
   '';
 
+  buildInputs = [ openssl db zlib uwimap html-tidy pam ];
+  nativeBuildInputs = [ perl ];
+
+  NIX_LDFLAGS = "-lpam";
+
   meta = {
     homepage = http://www-uxsup.csx.cam.ac.uk/~dpc22/prayer/;
     description = "Yet another Webmail interface for IMAP servers on Unix systems written in C";