Fix libva related compile errors

- Make h264.c compile with recent libva version by including va_compat.h
- Only enable libva if libva-x11 is installed
- Modified configure help text
  Previous help text suggested libva was only build when --with-libva
  was specified, while actual behavior is to build it by default.

Warning: THIS CODE IS UNTESTED. Lacking a h.264 capable VNC server
Also no attempt is made to support platforms not using X11

Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Fix compiler warnings libvncclient + gtkvncviewer

Fixes the following compiler warnings.

gtkvncviewer:

==
  CC       gtkvncviewer-gtkvncviewer.o
gtkvncviewer.c: In function ‘GtkDefaultLog’:
gtkvncviewer.c:591:2: warning: format not a string literal and no format arguments [-Wformat-security]
  fprintf (stdout, buf);
  ^
==

libvncclient:

==
  CC       rfbproto.lo
In file included from rfbproto.c:2376:0:
zrle.c: In function 'HandleZRLE8':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile8' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:37:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                                 ^
rfbproto.c:2364:22: note: in definition of macro 'CONCAT2'
 #define CONCAT2(a,b) a##b
                      ^
zrle.c:37:24: note: in expansion of macro 'CONCAT2E'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2385:0:
zrle.c: In function 'HandleZRLE16':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile16' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:37:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                                 ^
rfbproto.c:2364:22: note: in definition of macro 'CONCAT2'
 #define CONCAT2(a,b) a##b
                      ^
zrle.c:37:24: note: in expansion of macro 'CONCAT2E'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2387:0:
zrle.c: In function 'HandleZRLE15':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile15' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:37:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                                 ^
rfbproto.c:2364:22: note: in definition of macro 'CONCAT2'
 #define CONCAT2(a,b) a##b
                      ^
zrle.c:37:24: note: in expansion of macro 'CONCAT2E'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2396:0:
zrle.c: In function 'HandleZRLE32':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile32' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:37:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                                 ^
rfbproto.c:2364:22: note: in definition of macro 'CONCAT2'
 #define CONCAT2(a,b) a##b
                      ^
zrle.c:37:24: note: in expansion of macro 'CONCAT2E'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2398:0:
zrle.c: In function 'HandleZRLE24':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile24' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:37:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                                 ^
rfbproto.c:2364:22: note: in definition of macro 'CONCAT2'
 #define CONCAT2(a,b) a##b
                      ^
zrle.c:37:24: note: in expansion of macro 'CONCAT2E'
 #define HandleZRLETile CONCAT2E(HandleZRLETile,REALBPP)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2401:0:
zrle.c: In function 'HandleZRLE24Down':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile24Down' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:40:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT3E(HandleZRLETile,REALBPP,Down)
                                 ^
rfbproto.c:2366:24: note: in definition of macro 'CONCAT3'
 #define CONCAT3(a,b,c) a##b##c
                        ^
zrle.c:40:24: note: in expansion of macro 'CONCAT3E'
 #define HandleZRLETile CONCAT3E(HandleZRLETile,REALBPP,Down)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
In file included from rfbproto.c:2404:0:
zrle.c: In function 'HandleZRLE24Up':
zrle.c:201:5: warning: pointer targets in passing argument 2 of 'HandleZRLETile24Up' differ in signedness [-Wpointer-sign]
     int result=HandleZRLETile(client,buf,remaining,rx+i,ry+j,subWidth,subHeight);
     ^
zrle.c:43:33: note: expected 'uint8_t *' but argument is of type 'char *'
 #define HandleZRLETile CONCAT3E(HandleZRLETile,REALBPP,Up)
                                 ^
rfbproto.c:2366:24: note: in definition of macro 'CONCAT3'
 #define CONCAT3(a,b,c) a##b##c
                        ^
zrle.c:43:24: note: in expansion of macro 'CONCAT3E'
 #define HandleZRLETile CONCAT3E(HandleZRLETile,REALBPP,Up)
                        ^
zrle.c:79:12: note: in expansion of macro 'HandleZRLETile'
 static int HandleZRLETile(rfbClient* client,
            ^
==

Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Merge pull request #49 from maxnet/master

Fix libva related compile errors