[MEDIUM] errorfile: use a local file to feed error messages

It is now possible to read error messages from local files,
using the 'errorfile' keyword. Those files are read during
parsing, so there's no I/O involved. They make it possible
to return custom error messages with custom status and headers.
diff --git a/examples/errorfiles/400.http b/examples/errorfiles/400.http
new file mode 100644
index 0000000..e223e38
--- /dev/null
+++ b/examples/errorfiles/400.http
@@ -0,0 +1,9 @@
+HTTP/1.0 400 Bad request

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>400 Bad request</h1>
+Your browser sent an invalid request.
+</body></html>
+
diff --git a/examples/errorfiles/403.http b/examples/errorfiles/403.http
new file mode 100644
index 0000000..a67e807
--- /dev/null
+++ b/examples/errorfiles/403.http
@@ -0,0 +1,9 @@
+HTTP/1.0 403 Forbidden

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>403 Forbidden</h1>
+Request forbidden by administrative rules.
+</body></html>
+
diff --git a/examples/errorfiles/408.http b/examples/errorfiles/408.http
new file mode 100644
index 0000000..aafb130
--- /dev/null
+++ b/examples/errorfiles/408.http
@@ -0,0 +1,9 @@
+HTTP/1.0 408 Request Time-out

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>408 Request Time-out</h1>
+Your browser didn't send a complete request in time.
+</body></html>
+
diff --git a/examples/errorfiles/500.http b/examples/errorfiles/500.http
new file mode 100644
index 0000000..bb121e8
--- /dev/null
+++ b/examples/errorfiles/500.http
@@ -0,0 +1,9 @@
+HTTP/1.0 500 Server Error

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>500 Server Error</h1>
+An internal server error occured.
+</body></html>
+
diff --git a/examples/errorfiles/502.http b/examples/errorfiles/502.http
new file mode 100644
index 0000000..94b35d4
--- /dev/null
+++ b/examples/errorfiles/502.http
@@ -0,0 +1,9 @@
+HTTP/1.0 502 Bad Gateway

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>502 Bad Gateway</h1>
+The server returned an invalid or incomplete response.
+</body></html>
+
diff --git a/examples/errorfiles/503.http b/examples/errorfiles/503.http
new file mode 100644
index 0000000..48fde58
--- /dev/null
+++ b/examples/errorfiles/503.http
@@ -0,0 +1,9 @@
+HTTP/1.0 503 Service Unavailable

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>503 Service Unavailable</h1>
+No server is available to handle this request.
+</body></html>
+
diff --git a/examples/errorfiles/504.http b/examples/errorfiles/504.http
new file mode 100644
index 0000000..f925184
--- /dev/null
+++ b/examples/errorfiles/504.http
@@ -0,0 +1,9 @@
+HTTP/1.0 504 Gateway Time-out

+Cache-Control: no-cache

+Connection: close

+Content-Type: text/html

+

+<html><body><h1>504 Gateway Time-out</h1>
+The server didn't respond in time.
+</body></html>
+
diff --git a/examples/errorfiles/README b/examples/errorfiles/README
new file mode 100644
index 0000000..a882632
--- /dev/null
+++ b/examples/errorfiles/README
@@ -0,0 +1,9 @@
+These files are default error files that can be customized
+if necessary. They are complete HTTP responses, so that
+everything is possible, including using redirects or setting
+special headers.
+
+They can be used with the 'errorfile' keyword like this :
+
+    errorfile 503 /etc/haproxy/errors/503.http
+