Restore the BRE inter-bbs netmail attachment work-around from SBBSecho v2:

If the attached file begins with a '^', ignore/skip that character in the file
path. This should resolve the error reported by Ken  of Section One BBS:
ERROR line 850, attachment file not found: ^C:/SBBS/XTRN/BRE777/...

SBBSecho v2.x included this work-around and it was not included in the v3
re-factoring/re-write. Of course, BRE is doing something wrong and is totally
at fault here, but no one expects BRE to be fixed... ever. :-)

src/sbbs3/sbbsecho.c

@@ -840,6 +840,9 @@ int write_flofile(const char *infile, fidoaddr_t dest, bool bundle, bool use_out
 	if(flo_filename == NULL)
 		return -2;
 
+	if(*infile == '^')  /* work-around for BRE/FE inter-BBS attachment bug */
+		infile++;
+
 #ifdef __unix__
 	if(isalpha(infile[0]) && infile[1] == ':')	// Ignore "C:" prefix
 		infile += 2;