Add DEPENDS matching for the full dependency tree.

Previously pkgin would simply consider the latest available version of a
package and recurse into its dependency tree, but this could lead to
issues if it was later found that the latest version is not suitable for
DEPENDS.

This was shown most clearly by conflicts between net/samba (3.x) and
net/samba4 (4.x).  Packages that pulled in net/samba and a DEPENDS of
samba>=3.x<4.0 would eventually fail when trying to install devel/talloc
(a dependency of net/samba4) alongside net/samba as those two packages
both try to install include/talloc.h.

By correctly matching DEPENDS during the full tree scan, net/samba4 is
no longer considered and devel/talloc is no longer pulled in as a
dependency.

The implementation isn't ideal, and eventually will be replaced with
better logic, but the correct behaviour is desired first (along with
appropriate test cases), improvements second.

depends.c

@@ -37,9 +37,10 @@
 void
 full_dep_tree(const char *pkgname, const char *depquery, Plisthead *pdphead)
 {
-	Pkglist		*pdp;
-	int			level;
-	char		query[BUFSIZ] = "";
+	Pkglist		*pdp, *dep;
+	Plistnumbered	*dephead;
+	int		level;
+	char		query[BUFSIZ];
 
 	query[0] = '\0';
 	if (depquery == DIRECT_DEPS) {
@@ -95,7 +96,35 @@ full_dep_tree(const char *pkgname, const char *depquery, Plisthead *pdphead)
 				break;
 			/* set all this range to the current level */
 			pdp->level = level;
-			snprintf(query, BUFSIZ, depquery, pdp->name);
+
+			/*
+			 * If we're searching remote dependencies we need
+			 * to ensure that, when there are multiple versions
+			 * available, the one we pick matches DEPENDS.
+			 *
+			 * Process them in order and pick the highest version
+			 * that matches the dependency requirement.
+			 */
+			if (depquery == DIRECT_DEPS) {
+				snprintf(query, BUFSIZ,
+				    "SELECT FULLPKGNAME FROM REMOTE_PKG "
+				    "WHERE PKGNAME = '%s' "
+				    "ORDER BY FULLPKGNAME DESC;", pdp->name);
+				if ((dephead = rec_pkglist(query)) == NULL)
+					continue;
+				SLIST_FOREACH(dep, dephead->P_Plisthead, next) {
+					snprintf(query, BUFSIZ,
+					    EXACT_DIRECT_DEPS, dep->full);
+					if (pkg_match(pdp->depend, dep->full))
+						break;
+				}
+				free_pkglist(&dephead->P_Plisthead);
+				free(dephead);
+			} else {
+				/* LOCAL_REVERSE_DEPS */
+				snprintf(query, BUFSIZ, depquery, pdp->name);
+			}
+
 			/*
 			 * record pdp->name's direct dependencies in head
 			 * with level = 0