convert: if getting a file from Perforce fails try to get it one more time

When converting a particularly large Perforce changelist (especially with  some
big files), it is very likely to run into an intermittent network issue (e.g.
WSAECONNRESET or WSAETIMEDOUT) getting one of the files, which will result in
the entire changelist converting being aborted. Which can be quite unfortunate
since you might have waited hours getting all other files. To mitigate this
let's attempt to get the file one more time, escalating original exception
if that attempt fails.

hgext/convert/p4.py

@@ -196,6 +196,9 b' class p4_source(converter_source):'
     def getfile(self, name, rev):
         cmd = 'p4 -G print %s' \
             % util.shellquote("%s#%s" % (self.depotname[name], rev))
+
+        lasterror = None
+        while True:
         stdout = util.popen(cmd, mode='rb')
 
         mode = None
@@ -207,7 +210,14 b' class p4_source(converter_source):'
             data = d.get("data")
 
             if code == "error":
-                raise IOError(d["generic"], data)
+                    # if this is the first time error happened
+                    # re-attempt getting the file
+                    if not lasterror:
+                        lasterror = IOError(d["generic"], data)
+                        # this will exit inner-most for-loop
+                        break
+                    else:
+                        raise lasterror
 
             elif code == "stat":
                 action = d.get("action")
@@ -216,7 +226,8 b' class p4_source(converter_source):'
                 p4type = self.re_type.match(d["type"])
                 if p4type:
                     mode = ""
-                    flags = (p4type.group(1) or "") + (p4type.group(3) or "")
+                        flags = ((p4type.group(1) or "")
+                               + (p4type.group(3) or ""))
                     if "x" in flags:
                         mode = "x"
                     if p4type.group(2) == "symlink":
@@ -229,6 +240,11 b' class p4_source(converter_source):'
             elif code == "text" or code == "binary":
                 contents += data
 
+                lasterror = None
+
+            if not lasterror:
+                break
+
         if mode is None:
             return None, None