Honor the symbolic link option when copying files

Inspect source links without following them when COPYFILE_SYM is requested, before rejecting directories. This makes the documented option recreate link text instead of copying the referent, including dangling and directory links. Preserve requested link timestamps and report link-creation errors without overwriting the destination. Cover direct calls, destination directories, normal dereferencing and the existing rsync file caller.

test/Makefile.am

@@ -20,6 +20,7 @@ TESTS           =
 TESTS          += chomp
 TESTS          += copyfile
 TESTS          += fcopyfile
+TESTS          += copyfile-symlink
 TESTS          += dir
 TESTS          += fexist
 TESTS          += fisdir
@@ -41,3 +42,4 @@ TESTS          += which
 TESTS          += yorn
 
 check_PROGRAMS  = $(TESTS)
+copyfile_symlink_SOURCES = copyfile-symlink.c