Simplify string escapes

Treat backslash as a universal escape character: "\n" is a newline,
backslash escapes any non-alphanumeric character.

This affects some test cases that had "\," standing for backslash-comma.
With the new uniform treatment of backslashes, this needs to be "\\,".

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index 685106b..5f49d5f 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -328,7 +328,7 @@
 
 X509 CSR Information RSA with SHA-256, containing commas
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_SHA256_C:MBEDTLS_RSA_C:MBEDTS_X509_INFO
-mbedtls_x509_csr_info:"data_files/server1.req.commas.sha256":"CSR version   \: 1\nsubject name  \: C=NL, O=PolarSSL\, Commas, CN=PolarSSL Server 1\nsigned using  \: RSA with SHA-256\nRSA key size  \: 2048 bits\n"
+mbedtls_x509_csr_info:"data_files/server1.req.commas.sha256":"CSR version   \: 1\nsubject name  \: C=NL, O=PolarSSL\\, Commas, CN=PolarSSL Server 1\nsigned using  \: RSA with SHA-256\nRSA key size  \: 2048 bits\n"
 
 X509 CSR Information EC with SHA1
 depends_on:MBEDTLS_ECDSA_C:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_SHA1_C
@@ -413,7 +413,7 @@
 
 X509 Get Distinguished Name #5
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA1_C
-mbedtls_x509_dn_gets:"data_files/server1.commas.crt":"subject":"C=NL, O=PolarSSL\, Commas, CN=PolarSSL Server 1"
+mbedtls_x509_dn_gets:"data_files/server1.commas.crt":"subject":"C=NL, O=PolarSSL\\, Commas, CN=PolarSSL Server 1"
 
 X509 Get Modified DN #1
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA1_C
@@ -2950,7 +2950,7 @@
 
 X509 Get time (UTC invalid character in year)
 depends_on:MBEDTLS_X509_USE_C
-x509_get_time:MBEDTLS_ASN1_UTC_TIME:"0\1130231212Z":MBEDTLS_ERR_X509_INVALID_DATE:0:0:0:0:0:0
+x509_get_time:MBEDTLS_ASN1_UTC_TIME:"0\\1130231212Z":MBEDTLS_ERR_X509_INVALID_DATE:0:0:0:0:0:0
 
 X509 Get time (UTC invalid character in month)
 depends_on:MBEDTLS_X509_USE_C