[entropy.fetchers] do not generate two separate requests per download

It has been discovered that each download() call (urllib handler)
caused the code to generate two separete HTTP requests for the same
URL. This commit hopefully fixes it without causing any regression

lib/entropy/fetchers.py

@@ -586,33 +586,46 @@ class UrlFetcher(TextInterface):
         try:
             self.__remotesize = int(self.__remotefile.headers.get(
                 "content-length", -1))
-            self.__remotefile.close()
         except KeyboardInterrupt:
             self.__urllib_close(False)
             raise
-        except Exception:
+        except ValueError:
             pass
 
-        # handle user stupidity
         try:
+            # i don't remember why this is needed
+            # the whole code here is crap and written at
+            # scriptkiddie age, but still, it works (kinda).
             request = url
             if ((self.__startingposition > 0) and (self.__remotesize > 0)) \
                 and (self.__startingposition < self.__remotesize):
 
+                headers = {
+                    "Range" : "bytes=" + \
+                        str(self.__startingposition) + "-" + \
+                        str(self.__remotesize)
+                }
+                if url_protocol in ("http", "https"):
+                    headers['User-Agent'] = user_agent
+
                 try:
                     request = urlmod.Request(
                         url,
-                        headers = {
-                            "Range" : "bytes=" + \
-                                str(self.__startingposition) + "-" + \
-                                str(self.__remotesize)
-                        }
-                    )
+                        headers = headers)
                 except KeyboardInterrupt:
                     self.__urllib_close(False)
                     raise
                 except:
                     pass
+
+                # this will be replaced, close...
+                try:
+                    self.__remotefile.close()
+                except:
+                    pass
+                self.__remotefile = urlmod.urlopen(
+                    request, None, self.__timeout)
+
             elif self.__startingposition == self.__remotesize:
                 # all fine then!
                 self.__urllib_close(False)
@@ -625,7 +638,6 @@ class UrlFetcher(TextInterface):
                 # locally and file cannot be trusted (resumed)
                 self.__urllib_open_local_file("wb")
 
-            self.__remotefile = urlmod.urlopen(request, None, self.__timeout)
         except KeyboardInterrupt:
             self.__urllib_close(False)
             raise