convert-svnexternals: fix parsing of wrongly transformed SVN revisions

SVN revision numbers from svn:externals property, which are a multiple
of 1024 (2^10), are transformed by SubGit to contain a binary suffix
("k", "m" and "g" have been checked) in .gitsvnextmodules file.
These aren't valid revision numbers in SVN either.

Examples:
  1024 -> 1k
  2048 -> 2k
  1048576 -> 1m
  1049600 -> 1025k
  1073741824 -> 1g

This led to the following error:
    svn_rev = int(parsed_config[section]['revision'])
ValueError: invalid literal for int() with base 10: '1k'

Signed-off-by: Markus Heidelberg <markus.heidelberg@web.de>
Signed-off-by: Elijah Newren <newren@gmail.com>

README.md

@@ -308,7 +308,7 @@ But this comes with some nasty caveats and limitations:
 # Design rationale behind filter-repo
 
 None of the existing repository filtering tools did what I wanted;
-they all came up short for my needs.  No tool provided any of the
+they all came up short for my needs. No tool provided any of the
 first eight traits below I wanted, and no tool provided more than
 two of the last four traits either:
 

contrib/filter-repo-demos/convert-svnexternals

@@ -254,6 +254,21 @@ def get_absolute_svn_url(svnext_url, svn_root_url):
 
   return True, svnext_url
 
+def parse_revision_value(value):
+  """
+  Parse the value of key 'revision' from a .gitsvnextmodules file and return it
+  as integer.
+
+  Used to handle non-numeric values like 1k, 2k, 3k etc. added by SubGit
+  instead of 1024, 2048, 3072 etc., likewise 1m, 2m, ..., 1g, ...
+  """
+  suffix = value[-1]
+  if suffix in "kmg":
+    mult = {"k": 1024, "m": 1024**2, "g": 1024**3}
+    return int(value[0:-1]) * mult[suffix]
+  else:
+    return int(value)
+
 def add_submodule_tree_entry(commit, parsed_config, section):
   """
   Add a submodule entry to the tree of a Git commit.
@@ -271,7 +286,7 @@ def add_submodule_tree_entry(commit, parsed_config, section):
 
   # Get SVN revision
   if parsed_config.has_option(section, 'revision'):
-    svn_rev = int(parsed_config[section]['revision'])
+    svn_rev = parse_revision_value(parsed_config[section]['revision'])
   else:
     # TODO: revision has to be guessed according to commit timestamp, skip for now
     return False