common: support disabling python shebang rewriting

useful if there are special python-containing shebangs that should not
be rewritten, for example with Ghidra's embedded jython.

Manual.md

@@ -1630,6 +1630,8 @@ In most cases version is inferred from shebang, install path or build style.
 Only required for some multi-language
 applications (e.g., the application is written in C while the command is
 written in Python) or just single Python file ones that live in `/usr/bin`.
+If `python_version` is set to `ignore`, python-containing shebangs will not be rewritten.
+Use this only if a package should not be using a system version of python.
 
 Also, a set of useful variables are defined to use in the templates:
 

common/hooks/post-install/04-create-xbps-metadata-scripts.sh

@@ -272,7 +272,7 @@ _EOF
 		fi
 	fi
 
-	if [ -n "$python_version" ]; then
+	if [ -n "$python_version" ] && [ "$python_version" != ignore ]; then
 		pycompile_version=${python_version}
 	fi
 

common/hooks/pre-pkg/03-rewrite-python-shebang.sh

@@ -12,6 +12,10 @@ hook() {
 		pyver="$python_version"
 	fi
 
+	if [ "$python_version" = ignore ]; then
+		return
+	fi
+
 	if [ -n "$pyver" ]; then
 		default_shebang="#!/usr/bin/python${pyver%.*}"
 	fi