Fix header file usage -- there were many unnecessary header files included in

busybox.h which slowed compiles.  I left only what was needed and then fixed up
all the apps to include their own header files.  I also fixed naming for pwd.h
and grp.h functions.  Tested to compile and run with libc5, glibc, and uClibc.
 -Erik

findutils/find.c

@@ -26,6 +26,8 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <dirent.h>
+#include <string.h>
+#include <stdlib.h>
 
 
 static char *pattern = NULL;

findutils/grep.c

@@ -28,6 +28,8 @@
 #include <errno.h>
 #include "busybox.h"
 
+extern void xregcomp(regex_t *preg, const char *regex, int cflags);
+
 extern int optind; /* in unistd.h */
 extern int errno;  /* for use with strerror() */
 

findutils/which.c

@@ -22,7 +22,9 @@
  */
 
 #include "busybox.h"
+#include <string.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 extern int which_main(int argc, char **argv)
 {