compiler: use fully-qualified names for tracking functions

Function name now consists of 3 parts:
1) full package path
2) method receiver type (if any)
3) function name itself .

Fix #1150.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/compiler/analysis.go

@@ -113,14 +113,15 @@ func (c *codegen) analyzeFuncUsage() funcUsage {
 			case *ast.CallExpr:
 				switch t := n.Fun.(type) {
 				case *ast.Ident:
-					usage[t.Name] = true
+					usage[c.getIdentName("", t.Name)] = true
 				case *ast.SelectorExpr:
-					usage[t.Sel.Name] = true
+					name, _ := c.getFuncNameFromSelector(t)
+					usage[name] = true
 				}
 			case *ast.FuncDecl:
 				// exported functions are always assumed to be used
 				if isMain && n.Name.IsExported() {
-					usage[n.Name.Name] = true
+					usage[c.getFuncNameFromDecl(pkg.Path(), n)] = true
 				}
 			}
 			return true