patch 8.0.0416: setting v:progpath is not quite right

Problem:    Setting v:progpath is not quite right.
Solution:   On MS-Windows add the extension. On Unix use the full path for a
            relative directory. (partly by James McCoy, closes #1531)
diff --git a/src/os_unix.c b/src/os_unix.c
index 6220044..6c5955b 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3103,7 +3103,7 @@
 	{
 	    if (path != NULL)
 	    {
-		if (name[0] == '.')
+		if (name[0] != '/')
 		    *path = FullName_save(name, TRUE);
 		else
 		    *path = vim_strsave(name);
@@ -3142,7 +3142,7 @@
 	{
 	    if (path != NULL)
 	    {
-		if (buf[0] == '.')
+		if (buf[0] != '/')
 		    *path = FullName_save(buf, TRUE);
 		else
 		    *path = vim_strsave(buf);