Make 'build' field in rockspecs mandatory.

Rockspecs must have a 'build' field. If by any chance, it is not needed
(see #379), add this:

````lua
build = { type = "none" }
````

1 files changed, 12 insertions, 0 deletions

diff --git a/test/testfiles/no_build_table-0.1-1.rockspec b/test/testfiles/no_build_table-0.1-1.rockspec
new file mode 100644
index 00000000..5d79e9a0
--- /dev/null
+++ b/test/testfiles/no_build_table-0.1-1.rockspec
@@ -0,0 +1,12 @@
+package = "no_build_table"
+version = "0.1-1"
+source = {
+   -- any valid URL
+   url = "https://raw.github.com/keplerproject/luarocks/master/src/luarocks/build.lua"
+}
+description = {
+   summary = "A rockspec with no build field",
+}
+dependencies = {
+   "lua >= 5.1"
+}