Add non-IUPAC filter to FASTA quickcheck (#16)

Boot out FASTA files with spurious characters (such as `-`, `?` and other garbage), finally putting DIPI#38 (COG-UK/dipi-group#38) to rest.

bin/elan_fastacheck.py

@@ -32,6 +32,8 @@ def readfq(fp): # this is a generator function
             if last: # reach EOF before reading enough quality
                 yield name, seq, None # yield a fasta record instead
                 break
+
+iupac_chars = set("ACGTRYKMSWBDHVN")
 
 if len(sys.argv) != 3:
     sys.exit(1)
@@ -50,6 +52,8 @@ def readfq(fp): # this is a generator function
     sys.exit(1)
 if not seq:
     sys.exit(2)
+if any(base.upper() not in iupac_chars for base in seq):
+    sys.exit(65)
 if len(seq) < min_len:
     sys.exit(3)
 fasta_fh.close()