util: when bootstrapped, return self path as wrapper

Avoid reporting itself via the true path of the script; use
the wrapper instead. That is, instead of

```
Error: Argument missing. See '$HOME/.luarocks/lib/luarocks/rocks-5.3/luarocks/dev-1/bin/luarocks help install'.
```

report

```
Error: Argument missing. See '$HOME/.luarocks/bin/luarocks help install'.
```

See https://github.com/luarocks/luarocks/issues/952#issuecomment-449966779

1 files changed, 10 insertions, 1 deletions

diff --git a/src/luarocks/util.lua b/src/luarocks/util.lua
index 7f7ad80f..2d44c189 100644
--- a/src/luarocks/util.lua
+++ b/src/luarocks/util.lua
@@ -352,7 +352,16 @@ function util.this_program(default)
       cur = dbg.source
       i=i+1
    end
-   return last:sub(1,1) == "@" and last:sub(2) or last
+   local prog = last:sub(1,1) == "@" and last:sub(2) or last
+
+   -- Check if we found the true path of a script that has a wrapper
+   local lrdir, binpath = prog:match("^(.*)/lib/luarocks/rocks%-[0-9.]*/[^/]+/[^/]+(/bin/[^/]+)$")
+   if lrdir then
+      -- Return the wrapper instead
+      return lrdir .. binpath
+   end
+
+   return prog
 end
 
 function util.deps_mode_help(program)