Solaris 9 doesn't have setenv and unsetenv so add compat versions, based

on code from Dagobert Michelsen.

compat/setenv.c

@@ -0,0 +1,49 @@
+/* $Id: setenv.c,v 1.1 2010-05-19 21:31:39 nicm Exp $ */
+
+/*
+ * Copyright (c) 2010 Dagobert Michelsen
+ * Copyright (c) 2010 Nicholas Marriott <nicm@users.sourceforge.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "tmux.h"
+
+int
+setenv(const char *name, const char *value, unused int overwrite)
+{
+	char	buf[1024];
+
+	snprintf(buf, sizeof(buf), "%s=%s", name, value);
+	return (putenv(buf));
+}
+
+int
+unsetenv(const char *name)
+{
+	char  **envptr;
+	int	namelen;
+
+	namelen = strlen(name);
+	for (envptr = environ; *envptr != NULL; envptr++) {
+		if (strncmp(name, *envptr, namelen) == 0 &&
+		    ((*envptr)[namelen] == '=' || (*envptr)[namelen] == '\0'))
+			break;
+	}
+	for (; *envptr != NULL; envptr++)
+		*envptr = *(envptr + 1);
+	return (0);
+}