sparse-checkout: properly match escaped characters
In cone mode, the sparse-checkout feature uses hashset containment
queries to match paths. Make this algorithm respect escaped asterisk
(*) and backslash (\) characters.
Create dup_and_filter_pattern() method to convert a pattern by
removing escape characters and dropping an optional "/*" at the end.
This method is available in dir.h as we will use it in
builtin/sparse-checkout.c in a later change.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>