Prevent scp-style arguments from being mangled

An argument like me@example.com:/tmp/ is not something we should convert
into a Windows path; Use the absence of a slash before the colon as a
tell-tale that it is *not* a POSIX path list (exception: if the part
left of the colon is "." or "..").

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/cygwin/msys2_path_conv.cc

@@ -455,6 +455,8 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
 
     int starts_with_minus = 0;
     int starts_with_minus_alpha = 0;
+    int only_dots = *it == '.';
+    int has_slashes = 0;
     if (*it == '-') {
       starts_with_minus = 1;
       it += 1;
@@ -498,11 +500,17 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
                 if (ch == '/' && *(it2 + 1) == '/') {
                     return URL;
                 } else {
+                    if (!only_dots && !has_slashes)
+                        goto skip_p2w;
                     return POSIX_PATH_LIST;
                 }
             } else if (memchr(it2, '=', end - it) == NULL) {
                 return SIMPLE_WINDOWS_PATH;
             }
+        } else if (ch != '.') {
+            only_dots = 0;
+            if (ch == '/' || ch == '\\')
+                has_slashes = 1;
         }
     }