Merge branch 'sp/stream-clean-filter'

When running a required clean filter, we do not have to mmap the
original before feeding the filter.  Instead, stream the file
contents directly to the filter and process its output.

* sp/stream-clean-filter:
  sha1_file: don't convert off_t to size_t too early to avoid potential die()
  convert: stream from fd to required clean filter to reduce used address space
  copy_fd(): do not close the input file descriptor
  mmap_limit: introduce GIT_MMAP_LIMIT to allow testing expected mmap size
  memory_limit: use git_env_ulong() to parse GIT_ALLOC_LIMIT
  config.c: add git_env_ulong() to parse environment variable
  convert: drop arguments other than 'path' from would_convert_to_git()

t/t1050-large.sh

@@ -13,7 +13,7 @@ test_expect_success setup '
 	echo X | dd of=large2 bs=1k seek=2000 &&
 	echo X | dd of=large3 bs=1k seek=2000 &&
 	echo Y | dd of=huge bs=1k seek=2500 &&
-	GIT_ALLOC_LIMIT=1500 &&
+	GIT_ALLOC_LIMIT=1500k &&
 	export GIT_ALLOC_LIMIT
 '