Added configure options --prefix=PATH and --log=FILE.

A prefix is prepended to all relative names at configure stage.
There is no prefix by default.

A log file name can be relative.
The default log file name is "nginext.log".

auto/options

@@ -12,6 +12,9 @@ NXT_CFLAGS=
 NXT_CC_OPT=
 NXT_LD_OPT=
 
+NXT_PREFIX=
+NXT_LOG="nginext.log"
+
 NXT_DEBUG=NO
 
 NXT_INET6=YES
@@ -54,6 +57,9 @@ do
 
         --build-dir=*)                   NXT_BUILD_DIR="$value"              ;;
 
+        --prefix=*)                      NXT_PREFIX="$value"                 ;;
+        --log=*)                         NXT_LOG="$value"                    ;;
+
         --debug)                         NXT_DEBUG=YES                       ;;
 
         --no-ipv6)                       NXT_INET6=NO                        ;;
@@ -94,3 +100,14 @@ do
     NXT_CONFIGURE_OPTIONS="$NXT_CONFIGURE_OPTIONS $nxt_opt"
 
 done
+
+
+case "$NXT_PREFIX" in
+    ""|*/)  ;;
+     *)  NXT_PREFIX="$NXT_PREFIX/"  ;;
+esac
+
+case "$NXT_LOG" in
+    /*)  ;;
+     *)  NXT_LOG="$NXT_PREFIX$NXT_LOG"  ;;
+esac